U.S. patent application number 10/193684 was filed with the patent office on 2003-05-15 for driving circuit for an optical scanners.
Invention is credited to Sakai, Nobuaki.
Application Number | 20030090771 10/193684 |
Document ID | / |
Family ID | 27482432 |
Filed Date | 2003-05-15 |
United States Patent
Application |
20030090771 |
Kind Code |
A1 |
Sakai, Nobuaki |
May 15, 2003 |
Driving circuit for an optical scanners
Abstract
A driving circuit for an optical scanner includes an oscillation
driving device for oscillating a moving plate, an oscillation
detecting device for detecting the oscillating condition of the
moving plate, an oscillating frequency control device for
controlling the amplitude of a torsional oscillation of the moving
plate, and an oscillating amplitude control device for controlling
the amplitude of the torsional oscillation of the moving plate. The
driving circuit is thus constructed so that the oscillation of a
scanner can be controlled with a high degree of accuracy.
Inventors: |
Sakai, Nobuaki; (Tokyo,
JP) |
Correspondence
Address: |
PILLSBURY WINTHROP, LLP
P.O. BOX 10500
MCLEAN
VA
22102
US
|
Family ID: |
27482432 |
Appl. No.: |
10/193684 |
Filed: |
July 12, 2002 |
Current U.S.
Class: |
359/199.3 ;
359/224.1 |
Current CPC
Class: |
G02B 26/105 20130101;
G02B 7/1821 20130101 |
Class at
Publication: |
359/198 ;
359/199; 359/223; 359/224 |
International
Class: |
G02B 026/08 |
Foreign Application Data
Date |
Code |
Application Number |
Jul 13, 2001 |
JP |
2001-214178 |
Jul 27, 2001 |
JP |
2001-228114 |
Jul 27, 2001 |
JP |
2001-228113 |
Jul 27, 2001 |
JP |
2001-218112 |
Claims
What is claimed is:
1. A driving circuit for an optical scanner, comprising: a support;
a moving plate, at least one surface of which reflects light;
elastic members connecting the support and the moving plate; a pair
of magnets arranged in the proximity of the moving plate at preset
distances; a driving coil provided on the moving plate; and a
sensor coil provided on the moving plate, wherein the driving
circuit includes: a current supplying device connected to the
driving coil, supplying a current including at least an
alternating-current component to the driving coil; a detecting
device connected to the sensor coil, detecting an induced
electromotive force generated in the sensor coil to output a
detecting signal corresponding to the induced electromotive force;
and a control device for controlling the current supplied to the
driving coil by the current supplying device in accordance with the
detecting signal output by the detecting device.
2. A driving circuit for an optical scanner according to claim 1,
wherein the control device has an oscillating frequency control
device for controlling a frequency of torsional oscillation of the
moving plate; a gain circuit for applying gain inversely
proportional to the frequency of torsional oscillation of the
moving plate to the detecting signal, at least, in a frequency band
in the proximity of the frequency; and an amplitude control device
for controlling an oscillating amplitude of the torsional
oscillation of the moving plate in accordance with an output of the
gain circuit.
3. A driving circuit for an optical scanner, comprising: a support;
a moving plate, at least one surface of which reflects light;
elastic members connecting the support and the moving plate; a pair
of magnets arranged in the proximity of the moving plate at preset
distances; a driving coil provided on the moving plate; and a
sensor coil provided on the moving plate, wherein the driving
circuit includes: a current supplying device for supplying a
current including at least an alternating-current component to the
driving coil; a detecting device for detecting an induced
electromotive force generated in the sensor coil to output a
detecting signal corresponding to the induced electromotive force;
and a control device for controlling the current supplied to the
driving coil by the current supplying device in accordance with the
detecting signal output by the detecting device, the control device
having an oscillating frequency control device for controlling a
frequency of torsional oscillation of the moving plate; a gain
circuit for applying gain inversely proportional to the frequency
of torsional oscillation of the moving plate to the detecting
signal, at least, in a frequency band in the proximity of the
frequency; and an amplitude control device for controlling an
oscillating amplitude of the torsional oscillation of the moving
plate in accordance with an output of the gain circuit.
4. A driving circuit for an optical scanner according to claim 3,
wherein the oscillating frequency control device is a resonant
frequency follow-up control device for torsion-oscillating the
moving plate at a mechanical resonant frequency in accordance with
the detecting signal.
5. A driving circuit for an optical scanner according to claim 3 or
4, wherein the gain circuit is constructed with a first-order
low-pass filter which has a cut-off frequency much lower than the
frequency of torsional oscillation of the moving plate.
6. A driving circuit for an optical scanner according to claim 3 or
4, wherein the gain circuit is constructed with a first-order
band-pass filter which has a cut-off frequency much lower than the
frequency of torsional oscillation of the moving plate.
7. A driving circuit for an optical scanner, comprising: a support;
a moving plate, at least one surface of which reflects light;
elastic members connecting the support and the moving plate; a pair
of magnets arranged in the proximity of the moving plate at preset
distances; a driving coil provided on the moving plate; and a
sensor coil provided on substantially the same plane as the driving
coil of the moving plate, wherein the driving circuit includes: a
current supplying device for supplying a current including at least
an alternating-current component to the driving coil; a detecting
device for detecting an induced electromotive force generated in
the sensor coil; a mutual induction electromotive force generating
device for falsely generating a mutual induction electromotive
force caused in the sensor coil, independent of the driving coil
and the sensor coil, by the current including at least the
alternating-current component which flows through the driving coil;
a subtraction device for subtracting an output of the mutual
induction electromotive force generating device from an output of
the detecting device; and a control device for controlling a
torsional oscillation of the moving plate in accordance with an
output of the subtraction device.
8. A driving circuit for an optical scanner, comprising: a support;
a moving plate, at least one surface of which reflects light; an
elastic member connecting the support and the moving plate; a
magnet connected through the elastic member to the moving plate; a
driving coil provided to the support; and a sensor coil provided to
the support, wherein the driving circuit includes: a current
supplying device for supplying a current containing at least an
alternating-current component to the driving coil; a detecting
device for detecting an induced electromotive force generated in
the sensor coil; a mutual induction electromotive force generating
device for falsely generating a mutual induction electromotive
force caused in the sensor coil, independent of the driving coil
and the sensor coil, by the current containing at least an
alternating-current component which flows through the driving coil;
a subtraction device for subtracting an output of the mutual
induction electromotive force generating device from an output of
the detecting device; and a control device for controlling a
torsional oscillation of the moving plate in accordance with an
output of the subtraction device.
9. A driving circuit for an optical scanner according to claim 7,
wherein the mutual induction electromotive force generating device
has a first coil and a second coil which are provided on a fixed
substrate; a second current supplying device for supplying a
current containing at least an alternating-current component to the
first coil; and a second detecting device for detecting an induced
electromotive force generated in the second coil, the subtraction
device subtraction-processing the output of the detecting device
and an output of the second detecting device.
10. A driving circuit for an optical scanner according to claim 8,
wherein the mutual induction electromotive force generating device
has a first coil and a second coil which are provided on a fixed
substrate; a second current supplying device for supplying a
current containing at least an alternating-current component to the
first coil; and a second detecting device for detecting an induced
electromotive force generated in the second coil, the subtraction
device subtraction-processing the output of the detecting device
and an output of the second detecting device.
11. A driving circuit for an optical scanner according to claim 9
or 10, further including a first gain circuit increasing or
decreasing a current to be supplied through the second current
supplying device and a second gain circuit increasing or decreasing
an output of the second detecting device.
12. A driving circuit for an optical scanner according to claim 7
or 8, wherein the mutual induction electromotive force generating
device falsely generates the mutual induction electromotive force
caused in the sensor coil, independent of the driving coil and the
sensor coil, in accordance with the current supplied to the driving
coil.
13. A driving circuit for an optical scanner according to claim 9
or 10, wherein a mutual inductance caused by the driving coil and
the sensor coil is practically equalized to a mutual inductance by
the first coil and the second coil.
14. A driving circuit for an optical scanner according to claim 13,
wherein the first coil is configured into substantially the same
structure and shape as the driving coil, the second coil is
configured into substantially the same structure and shape as the
sensor coil, the second current supplying device is constructed
similar to the current supplying device, and the second detecting
device is constructed similar to the detecting device.
15. A driving circuit for an optical scanner according to claim 12,
wherein the mutual induction electromotive force generating device
has a phase shifting device for shifting a phase of a signal
produced in accordance with the current supplied to the driving
coil and a variable gain device for increasing or decreasing the
signal produced in accordance with the current supplied to the
driving coil.
16. A driving circuit for an optical scanner according to claim 15,
wherein the control device has at least one of an amplitude control
device for continuously controlling an amplitude of the torsional
oscillation of the moving plate in accordance with a result of the
subtraction device and a frequency control device for continuously
controlling a frequency of the torsional oscillation of the moving
plate.
17. A driving circuit for an optical scanner, comprising: a
support; a moving plate, at least one surface of which reflects
light; elastic members connecting the support and the moving plate;
a pair of magnets arranged in the proximity of the moving plate at
preset distances; a driving coil provided on the moving plate; and
a sensor coil provided on substantially the same plane as the
driving coil of the moving plate, wherein the driving circuit
includes: an oscillation driving device for supplying a current
containing at least an alternating-current component to the driving
coil to execute a torsional oscillation of the moving plate within
a preset angle; an oscillation detecting device for detecting an
induced electromotive force generated in the sensor coil, provided
with an electromotive force detecting device for outputting a
detecting signal corresponding thereto; an oscillating frequency
control device for controlling a frequency of the torsional
oscillation; a first oscillating amplitude control device for
controlling an amplitude of the torsional oscillation in accordance
with the detecting signal output by the oscillation detecting
device; and a second oscillating amplitude control device for
controlling an oscillating condition with each of frequency
components except for a frequency of the torsional oscillation in
accordance with the detecting signal output by the oscillation
detecting device.
18. A driving circuit for an optical scanner, comprising: a
support; a moving plate, at least one surface of which reflects
light; an elastic member connecting the support and the moving
plate; a magnet connected through the elastic member to the moving
plate; a driving coil provided to the support; and a sensor coil
provided to the support, wherein the driving circuit includes: an
oscillation driving device for supplying a current containing at
least an alternating-current component to the driving coil to
execute a torsional oscillation of the moving plate within a preset
angle; an oscillation detecting device for detecting an induced
electromotive force generated in the sensor coil, provided with an
electromotive force detecting device for outputting a detecting
signal corresponding thereto; an oscillating frequency control
device for controlling a frequency of the torsional oscillation; a
first oscillating amplitude control device for controlling an
amplitude of the torsional oscillation in accordance with the
detecting signal output by the oscillation detecting device; and a
second oscillating amplitude control device for controlling an
oscillating condition with each of frequency components except for
a frequency of the torsional oscillation in accordance with the
detecting signal output by the oscillation detecting device.
19. A driving circuit for an optical scanner according to claim 17
or 18, wherein the second oscillating amplitude control device has
a low-pass filter for extracting a frequency component lower than
the frequency of the torsional oscillation from the detecting
signal and a low-frequency oscillation eliminating device for
controlling the oscillating condition of the moving plate so that
an output thereof becomes zero.
20. A driving circuit for an optical scanner according to claim 17
or 18, wherein the oscillating frequency control device is provided
with a resonant frequency follow-up control device for executing
the torsional oscillation of the moving plate at a mechanical
resonant frequency in accordance with a detecting signal.
21. A driving circuit for an optical scanner, comprising: a
support; a moving plate, at least one surface of which reflects
light; elastic members connecting the support and the moving plate;
a pair of magnets arranged in the proximity of the moving plate at
preset distances; a driving coil provided on the moving plate; and
a sensor coil provided on the moving plate, wherein the driving
circuit includes: an oscillation driving device for supplying a
current containing at least an alternating-current component to the
driving coil to execute a torsional oscillation of the moving plate
within a preset angle; an oscillation detecting device for
detecting an oscillating condition of the moving plate in
accordance with an induced electromotive force generated in the
sensor coil; an amplitude control device for controlling an
amplitude of an oscillation of the moving plate in accordance with
an output of the oscillation detecting device; and a frequency
control device for controlling an oscillating frequency of the
moving plate, the oscillation detecting device having: a
constant-voltage source connected in series to the sensor coil; a
voltage detecting device for detecting voltages created at both
terminals of a series circuit comprised of the sensor coil and the
constant-voltage source to output signals corresponding thereto; a
constant-voltage eliminating device for outputting a signal in
which a constant-voltage component is eliminated from an output of
the voltage detecting device; and a constant-voltage extracting
device for extracting the constant-voltage component from the
output of the voltage detecting device to output a signal
corresponding thereto.
22. A driving circuit for an optical scanner, comprising: a
support; a moving plate, at least one surface of which reflects
light; an elastic member connecting the support and the moving
plate; a magnet connected through the elastic member to the moving
plate; a driving coil provided to the support; and a sensor coil
provided to the support, wherein the driving circuit includes: an
oscillation driving device for supplying a current containing at
least an alternating-current component to the driving coil to
execute a torsional oscillation of the moving plate within a preset
angle; an oscillation detecting device for detecting an oscillating
condition of the moving plate in accordance with an induced
electromotive force generated in the sensor coil; an amplitude
control device for controlling an amplitude of an oscillation of
the moving plate in accordance with an output of the oscillation
detecting device; and a frequency control device for controlling an
oscillating frequency of the moving plate, the oscillation
detecting device having: a constant-voltage source connected in
series to the sensor coil; a voltage detecting device for detecting
voltages created at both terminals of a series circuit comprised of
the sensor coil and the constant-voltage source to output signals
corresponding thereto; a constant-voltage eliminating device for
outputting a signal in which a constant-voltage component is
eliminated from an output of the voltage detecting device; and a
constant-voltage extracting device for extracting the
constant-voltage component from the output of the voltage detecting
device to output a signal corresponding thereto.
23. A driving circuit for an optical scanner according to claim 21
or 22, wherein the oscillation detecting device is further provided
with a division device for dividing an output of the
constant-voltage eliminating device by an output of the
constant-voltage extracting device.
24. A driving circuit for an optical scanner, comprising: a
support; a moving plate, at least one surface of which reflects
light; an elastic member connecting the support and the moving
plate; a magnet connected through the elastic member to the moving
plate; a driving coil provided to the support; and a sensor coil
provided to the support, wherein the driving circuit includes: an
oscillation driving device for supplying a current containing at
least an alternating-current component to the driving coil to
execute a torsional oscillation of the moving plate within a preset
angle; an oscillation detecting device for detecting an oscillating
condition of the moving plate in accordance with an induced
electromotive force generated in the sensor coil; an amplitude
control device for controlling an amplitude of an oscillation of
the moving plate in accordance with an output of the oscillation
detecting device; and a frequency control device for controlling an
oscillating frequency of the moving plate.
25. A driving circuit for an optical scanner according to claim 24,
wherein the oscillation detecting device having: a constant-voltage
source connected in series to the sensor coil; a voltage detecting
device for detecting voltages created at both terminals of a series
circuit comprised of the sensor coil and the constant-voltage
source to output signals corresponding thereto; a constant-voltage
eliminating device for outputting a signal in which a
constant-voltage component is eliminated from an output of the
voltage detecting device; and a constant-voltage extracting device
for extracting the constant-voltage component from the output of
the voltage detecting device to output a signal corresponding
thereto.
26. A driving circuit for an optical scanner. according to claim
25, wherein the oscillation detecting device is further provided
with a division device for dividing an output of the
constant-voltage eliminating device by an output of the
constant-voltage extracting device.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] This invention relates to a driving circuit for an optical
scanner in which light from a light source is reflected and an
optical scanner performing a one- or two-dimensional scan with this
reflected light is driven.
[0003] 2. Description of the Related Art
[0004] Some of conventional optical scanners are disclosed in
Japanese Patent Kokai Nos. Hie 7-175005 and Hie 10-123449. Each of
these optical scanners is fabricated by semiconductor manufacturing
technology and has the features of compactness and small
thickness.
[0005] FIG. 1 shows a diagram for illustrating an operating
principle of the optical scanner. As shown in this figure, the
optical scanner includes a mirror portion 101 in which a coil
pattern (a driving coil 102) is provided parallel with a mirror
face 101a; spring portions 104a and 104b for oscillating the mirror
portion 101; and permanent magnets 105a and 105b arranged close to
the mirror portion 101, for producing a magnetic field nearly
parallel with the mirror face 101a where the mirror portion 101 is
in a stationary state. The spring portions 104a and 104b are
connected to a support, not shown, to be fixed to an arbitrary
member. By supplying an alternating current (of a frequency t) to
the driving coil 102, a force obeying the left-hand rule is
generated in a direction normal to the mirror face 101a to
oscillate the mirror portion 101 at the frequency f.
[0006] When the alternating current is represented by I (=I.sub.0
sin (2.pi.ft)), the strength of the magnetic field by H (a magnetic
flux density B), the number of turns of the coil by N, the area of
the coil by S, and a vacuum magnetic constant by .mu..sub.0, an
oscillating angle .theta. and a generating force F in this case
have the relation expressed by the following equation:
F=.mu..sub.0NHSI.sub.0 sin(2.pi.ft).multidot.cos .theta. (1)
[0007] The oscillating angle .theta. can be found by solving the
following equation of motion: 1 = - k - D . + F J ( 2 )
[0008] Here, k is a torsion spring constant of the spring portion
and has the relation of k=(2.pi.f.sub.c).sup.2, where f.sub.c is a
mechanical resonant frequency of the optical scanner, D is an
attenuation coefficient, and J is the moment of inertia of the
optical scanner.
[0009] The relation between the oscillating angle .theta. and the
frequency f of the alternating current, in which the oscillating
angle .theta. is thought of as small, can be expressed from Eqs.
(1) and (2) by the following equation: 2 ( f ) = 0 NHSI 0 J 1 { k -
( 2 f ) 2 } 2 + D 2 ( 2 f ) 2 ( 3 )
[0010] FIG. 2A shows a plot of Eq. (3). As shown in FIG. 2A, the
maximum oscillating angle (oscillating amplitude) is obtained when
the driving frequency f of the alternating current is caused to
coincide with the mechanical resonant frequency f.sub.c.
[0011] From this reason, it is a common practice for the drive of
the optical scanner to cause the frequency of a driving signal to
coincide with the mechanical resonant frequency of the optical
scanner.
[0012] In order to stabilize the drive of the optical scanner
mentioned above, it is necessary to provide a sensor for detecting
the oscillating condition of the optical scanner. In the optical
scanner using such a sensor, as disclosed, for example, in Japanese
Patent Kokai No. Hie 11-242180, it is known that, in addition to
the structure of FIG. 1, a coil pattern (hereinafter referred to as
a sensor coil 103), different from the driving coil 102, is
provided nearly concentrically on the same plane as the driving
coil 102 in the mirror portion 101 (see FIG. 3), and when the
mirror portion 101 is oscillated, an electromotive force generated
by the interlinkage of the sensor coil 103 with the magnetic field
is detected and thereby the oscillating condition is detected.
[0013] Here, in the technique of detecting the oscillating
condition of the optical scanner of the structure mentioned above,
an electromotive force V.sub.r generated in the sensor coil 103 is
given by the following equation:
V.sub.r=N.sub.sBS.sub.s{dot over (.theta.)}.multidot.cos .theta.
(4)
[0014] where N.sub.s is the number of turns of the sensor coil, B
is the magnetic flux density, and S.sub.s is the area of the sensor
coil.
[0015] Now, consider the case where the optical scanner is driven
with the mechanical resonant frequency f.sub.c. When the driving
signal is expressed as I=I.sub.0 sin (2.pi.f.sub.ct), the
oscillation of the optical scanner is retarded in phase by
90.degree. with respect to the driving signal, thus giving
.theta.=-.theta..sub.0.multidot.cos(2.pi.f.sub.ct) (5)
[0016] Therefore, the electromotive force V.sub.r expressed by Eq.
(4), in which the oscillating angle .theta. (.theta..sub.0) is
thought of as small, can be approximated by the following equation:
3 V r = N s B S s 0 2 f c sin ( 2 f c t ) cos { - 0 cos ( 2 f c t )
} N s B S s 0 2 f c sin ( 2 f c t ) ( 6 )
[0017] Whereby, it is found that the electromotive force generated
in the sensor coil is 90.degree. ahead in phase with respect to the
oscillation of the optical scanner. (Also, if the connections of
both ends of the coil are replaced, the sign of the electromotive
force will reverse and the phase will be retarded by 90.degree.,
and the following description is given on the basis of this
practice.) Thus, in the resonant frequency drive, the phase
relations of the driving signal, the drive of the optical scanner,
and the electromotive force of the sensor coil (a sensor signal)
are as shown in FIGS. 4A, 4B, and 4C, respectively, and the driving
signal (FIG. 4A) coincides in phase with the sensor signal (FIG.
4C).
[0018] Here, where the optical scanner is driven at an arbitrary
frequency which is much lower than the resonant frequency, the
oscillation of the optical scanner, when the driving signal is
expressed as I=I.sub.0 sin(2.pi.ft), coincides in phase with the
driving signal, thus giving
.theta.=-.theta..sub.0.multidot.sin(2.pi.ft) (7)
[0019] Therefore, the electromotive force V.sub.r expressed by Eq.
(4), in which the oscillating angle .theta. (.theta..sub.0) is
thought of as small, can be approximated by the following equation:
4 V r = N s B S s 0 2 f cos ( 2 f t ) cos { 0 sin ( 2 f t ) } N s B
S s 0 2 f cos ( 2 f t ) ( 8 )
[0020] A common control driving circuit for operating the optical
scanner with stability is disclosed in Japanese Patent Kokai No.
Hie 09-101474. This control driving circuit has a frequency
follow-up control function (a positive feedback control function)
for always driving the optical scanner with the resonant frequency
and an amplitude control function (a negative feedback control
function) for operating the optical scanner with stability at a
desired oscillating amplitude.
[0021] However, when the control drive of the optical scanner with
the sensor is made, the following problem {circle over (1)}
arises.
[0022] Specifically, the sensor signal (the electromotive force
produced in the sensor coil), as shown in Eq. (6) or (8), is
proportional to the driving frequency. Consequently, when resonant
frequency follow-up control such as that described in Kokai No. Hie
09-101474 is made, the mechanical resonant frequency of the optical
scanner fluctuates due to changes of ambience and with age, and
thereby the sensor signal is changed, that is, a sensor sensitivity
as an oscillating angle sensor is varied, although the oscillating
angle is not altered. This gives rise to a vital problem for
high-precision amplitude control. Even when the optical scanner is
driven at a frequency which is much lower than the resonant
frequency, the sensor signal (sensor sensitivity) varies with the
driving frequency, and thus the amplitude control becomes
difficult.
[0023] Briefly described here is a fundamental control driving
technique of the conventional optical scanner. An optical scanner 1
is controlled by circuitry shown in FIG. 5. In FIG. 5, from an
operating controller such as a PC, not shown, a control signal
which is a command value of the desired driving condition of the
optical scanner 1, such as the oscillating amplitude (oscillating
angle) or oscillating frequency of the optical scanner 1, is
supplied to a control circuit 4. The control circuit 4, when
receiving the control signal, outputs a driving command signal
V.sub.d to a driving circuit 2. The driving circuit 2 outputs a
driving signal (the alternating current) to the driving coil 102 in
accordance with the driving command signal V.sub.d. The optical
scanner 1 is thus oscillated at desired oscillating angle and
oscillating frequency. In this case, at both ends of the sensor
coil is 5103, when the sensor coil 103 is interlinked with the
magnetic field produced by the permanent magnets 105a and 105b, the
electromotive force (the sensor signal) is generated. This
electromotive force (the sensor signal) is feedbacked to the
control circuit 4 as a detecting signal V.sub.s detected by a
detecting circuit 3. In the control circuit 4, the detecting signal
V.sub.s is monitored so that when the oscillating amplitude (the
oscillating angle) or oscillating frequency of the optical scanner
1 is out of a desired value, the driving command signal V.sub.d
output to the driving circuit 2 is compensated. In this way, the
optical scanner 1 can be controlled and driven with stability.
[0024] Subsequently, general constructions of the driving circuit 2
and a detecting circuit 3-a are shown in FIG. 6. As shown in this
figure, the driving circuit 2 includes an operational amplifier 201
and a resistance element (R0) 202 so that they convert the driving
command signal V.sub.d into the driving signal (the alternating
current).
[0025] Here, when the driving signal supplied to the driving coil
102 is expressed as I=I.sub.0 sin(2.pi.f.sub.ct)=I.sub.0 sin
(.omega..sub.ct), the relation between the driving command signal
V.sub.d and the driving signal (the alternating current) is given
by the following equation:
V.sub.d=R.sub.0.multidot.I=R.sub.0.multidot.I.sub.0
sin(.omega..sub.ct) (9)
[0026] The detecting circuit 3-a includes an operational amplifier
301, a resistance element (R1) 302, a resistance element (R1) 303,
a resistance element (R2) 304, and a resistance element (R2) 305 so
that they convert the electromotive force (the sensor signal) into
the detecting signal V.sub.s.
[0027] Here, when the electromotive force is denoted by V.sub.r,
the resistance value of the sensor coil is denoted by R.sub.sens,
and the self-inductance and wiring capacity of the sensor coil 103
are assumed to be negligible, the relation between the
electromotive force V.sub.r and the detecting signal V.sub.s is
given by the following equation: 5 V s = - 2 R 2 2 R 1 + R sens V r
( 10 )
[0028] However, the conventional optical scanner has the following
problem {circle over (2)}.
[0029] Specifically, when the driving signal (the alternating
current) I is supplied to the driving coil, as shown in FIG. 7, a
magnetic field H.sub.1 proportional to the driving signal I is
produced in a direction perpendicular to the driving coil. In this
case, since the conventional optical scanner is such that the
driving coil and the sensor coil are nearly concentric and are
provided on the same plane, an electromotive force (hereinafter
referred to as a mutual induction electromotive force) e.sub.r
attributable to a change of the strength of the magnetic field
H.sub.1 is generated in the sensor coil. The mutual induction
electromotive force e.sub.r is proportional to a mutual inductance
M caused by the driving coil and the sensor coil and the time
differential of the driving signal I, and when the driving signal
is expressed as I=I.sub.0 sin(2.pi.f.sub.ct)=I.sub.0
sin(.omega..sub.ct) and a factor of proportionality is denoted by
.alpha., it can be expressed by the following equation: 6 e r = M I
. ( or I t ) = M c I 0 cos ( c t ) ( 11 )
[0030] From the above description, it is found that the
electromotive force (the sensor signal) actually generated in the
sensor coil is not only the electromotive force V.sub.r expressed
by Eq. (4), but also the sum with the mutual induction
electromotive force e.sub.r expressed by Eq. (11), namely
(V.sub.r+e.sub.r).
[0031] Thus, the true detecting signal V.sub.s is given from Eq.
(10) by the following equation: 7 V s = - 2 R 2 2 R 1 + R sens ( V
r + e r ) ( 12 )
[0032] and a distorted signal is obtained due to the term of the
mutual induction electromotive force e.sub.r. With this signal, it
is difficult to control the oscillating amplitude of the optical
scanner with a high degree of accuracy. Also, the phase relations
of the driving signal in the resonant frequency drive, the mutual
induction electromotive force e.sub.r, and a true electromotive
force (sensor signal) are shown in FIGS. 8A, 8B, and 8C,
respectively, and the actual oscillating condition and the sensor
signal will be out of phase. This signifies that it becomes
difficult to control the oscillating frequency of the optical
scanner with a high degree of accuracy.
[0033] The control driving circuit of the conventional optical
scanner has the following problem {circle over (3)}.
[0034] Specifically, the optical scanner mentioned above,
theoretically, executes an oscillating motion with single frequency
as in Eq. (5) or (7), but actually executes the oscillating motion
with a plurality of frequency components, as shown in Eq. (13) or
(14) to be described blow, under the influence of an electric
noise, mechanical vibrating noise, or magnetic noise.
.theta.(t)=-.theta..sub.0{1+.alpha.
sin(2.pi.f.sub..alpha.t+.theta..sub..a-
lpha.)}cos(2.pi.f.sub.ct)+.beta.
sin(2.pi.f.sub..beta.t+.theta..sub..beta.- ) (13)
[0035] 8 ( t ) = 0 { 1 + sin ( 2 f t + ) } sin ( 2 f t ) ( I ) +
sin ( 2 f t + ) ( II ) ( 14 )
[0036] Eq. (13) or (14) is briefly described below. The first term
indicated by (I), as shown in FIG. 9A, exhibits a state where an
amplitude-modulation noise is produced with respect to a desired
oscillating motion of the optical scanner. The second term
indicated by (II), as shown in FIG. 9B, exhibits a state where the
center of oscillation fluctuates (alternating offset is produced)
with respect to the oscillating motion of the optical scanner. An
actual oscillating motion of the optical scanner, as shown in FIG.
9C, is in a state where the oscillations of (I) and (II) are
superimposed. (Also, in the present invention, the noise of a
higher frequency than in the desired oscillating motion of the
optical scanner is thought of as negligible. This is because, as
seen from the oscillating characteristics of FIGS. 2A and 2B, it is
hard to affect the oscillating motion of the optical scanner by the
noise of a high frequency.)
[0037] Since the control driving circuit of the conventional
optical scanner has an amplitude control function for operating the
optical scanner with stability at a desired oscillating amplitude,
the amplitude-modulation noise of (I) can be eliminated. The
optical scanner, however, is constructed so that the fluctuation of
the center of the oscillation of (II) cannot be eliminated. As
such, there is the problem that the optical scanner cannot be
driven with a high degree of accuracy.
[0038] Here, referring back to FIG. 6, the relation between the
driving command signal V.sub.d and the driving signal I (the
alternating current) is given by the following equation:
I=V.sub.d/R.sub.0 (15)
[0039] Although each of a detecting circuit 3-b shown in FIG. 10
and a detecting circuit 3-c in FIG. 11 cannot be expected to
provide a detecting function with a high degree of accuracy as in
the detecting circuit 3-a of a differential type, it is effective
as the detecting circuit and thus its construction is briefly
described below.
[0040] The detecting circuit 3-b shown in FIG. 10 includes an
operational amplifier 310, a resistance element (R3) 311, and a
resistance element (R4) 312 so that they convert the electromotive
force (the sensor signal) into the detecting signal V.sub.s.
[0041] Here, again, when the electromotive force is denoted by
V.sub.r, the resistance value of the sensor coil is denoted by
R.sub.sens, and the self-inductance and wiring capacity of the
sensor coil 103 are assumed to be negligible, the relation between
the electromotive force V.sub.r and the detecting signal V.sub.s in
the detecting circuit 3-b can be expressed as 9 V s = R 4 R 3 + R
sens V r ( 16 )
[0042] The detecting circuit 3-c shown in FIG. 11 includes an
operational amplifier 320 and a resistance element (R5) 321 so that
they convert the electromotive force (the sensor signal) into the
detecting signal V.sub.s.
[0043] Here, again, when the electromotive force is denoted by
V.sub.r, the resistance value of the sensor coil is denoted by
R.sub.sens, and the self-inductance and wiring capacity of the
sensor coil 103 are assumed to be negligible, the relation between
the electromotive force V.sub.r and the detecting signal V.sub.s in
the detecting circuit 3-c can be expressed as 10 V s = R 5 R 5 + R
sens V r ( 17 )
[0044] However, the driving circuit of the conventional optical
scanner has the following problem {circle over (4)}. As shown in
Eqs. (10), (16) and (17), the detecting signal V.sub.s is provided
with the resistance value of the sensor coil, and when the
resistance value of the sensor coil fluctuates due to a change of
ambient and with age, the detecting signal V.sub.s is changed
thereby. Furthermore, the sensor coil is placed close to the
driving coil, and it is conceivable that the sensor coil is
affected by the generation of heat of the driving coil. When the
detecting signal V.sub.s is changed by the fluctuation of the
resistance value of the sensor coil, it is impossible to detect the
oscillating condition of the optical scanner with a high degree of
accuracy.
SUMMARY OF THE INVENTION
[0045] In order to solve the problem {circle over (1)}, it is a
first object of the present invention to provide a driving circuit
for an optical scanner in which amplitude control can be attained
with a high degree of accuracy without undergoing the influence of
a change in the driving frequency of the optical scanner.
[0046] In order to solve the problem {circle over (2)}, it is a
second object of the present invention to provide a driving circuit
for an optical scanner in which an operation can be performed with
a high degree of accuracy at desired amplitude and frequency by
eliminating the mutual induction electromotive force generated in
the sensor coil.
[0047] In order to solve the problem {circle over (3)}, it is a
third object of the present invention to provide a driving circuit
for an optical scanner in which the fluctuation of the center of
the oscillation of the optical scanner can be eliminated and
amplitude control can be attained with a high degree of
accuracy.
[0048] In order to solve the problem {circle over (4)}, it is a
fourth object of the present invention to provide a driving circuit
for an optical scanner in which the oscillating condition of the
optical scanner can be detected without undergoing the influence of
the fluctuation of the resistance value of the sensor coil and
amplitude control can be attained with a high degree of
accuracy.
[0049] In order to achieve the first object, the driving circuit
for an optical scanner according to present invention includes a
support to be fixed to an arbitrary member; a moving plate, at
least one surface of which reflects light; elastic members
connecting the support and the moving plate; magnets arranged close
to the moving plate at preset distances; a driving coil provided on
the moving plate; and a sensor coil provided on the moving plate.
In this case, the driving circuit has a current supplying device
for supplying a current containing at least an alternating-current
component to the driving coil; a detecting device for detecting an
induced electromotive force generated in the sensor coil to output
a detecting signal corresponding to the induced electromotive
force; and a control device for controlling the current supplied to
the driving coil by the current supplying device in accordance with
the detecting signal output by the detecting device. The control
device has an oscillating frequency control device for controlling
the frequency of torsional oscillation of the moving plate; a gain
circuit for applying gain inversely proportional to the frequency
of torsional oscillation of the moving plate to the detecting
signal, at least, in the frequency band close to the frequency; and
an amplitude control device for controlling the oscillating
amplitude of the torsional oscillation of the moving plate in
accordance with the output of the gain circuit.
[0050] According to the present invention constructed as mentioned
above, the gain inversely proportional to the frequency of
torsional oscillation of the moving plate is applied to the
detecting signal proportional to the frequency, and thereby the
oscillating amplitude of the torsional oscillation of the moving
plate without undergoing the influence of a change in the driving
frequency of the optical scanner. Consequently, the amplitude
control can be attained with a high degree of accuracy.
[0051] In order to achieve the above object, the driving circuit
for an optical scanner according to the present invention is such
that the oscillating frequency control device is a resonant
frequency follow-up control device for torsion-oscillating the
moving plate at the mechanical resonant frequency in accordance
with the detecting signal.
[0052] According to the present invention constructed as mentioned
above, the optical scanner can be torsion-oscillated at the
mechanical resonant frequency, and it becomes possible to make the
detection of the oscillating amplitude which is not affected by the
fluctuation of the mechanical resonant frequency of the optical
scanner. Consequently, the amplitude control can be attained with a
high degree of accuracy.
[0053] Further, in order to achieve the above object, the driving
circuit for an optical scanner according to the present invention
is such that the gain circuit is constructed with a first-order
low-pass filter which has a cut-off frequency much lower than the
frequency of torsional oscillation of the moving plate.
[0054] According to the present invention constructed mentioned
above, the gain inversely proportional to the frequency of
torsional oscillation of the moving plate is applied to the
detecting signal proportional to the frequency, and gain in a low
frequency band can be suppressed. The amplitude control can thus be
attained with stability.
[0055] Still further, in order to achieve the above object, the
driving circuit for an optical scanner according to the present
invention is such that the gain circuit is constructed with a
first-order band-pass filter which has a cut-off frequency much
lower than the frequency of torsional oscillation of the moving
plate.
[0056] According to the present invention constructed mentioned
above, the gain inversely proportional to the frequency of
torsional oscillation of the moving plate is applied to the
detecting signal proportional to the frequency, and a noise in the
low frequency band can be reduced. The amplitude control can thus
be attained with a high degree of accuracy.
[0057] In order to achieve the second object, the driving circuit
for an optical scanner according to the present invention includes
a support to be fixed to an arbitrary member; a moving plate, at
least one surface of which reflects light; elastic members
connecting the support and the moving plate; a pair of magnets
arranged close to the moving plate at preset distances; a driving
coil provided on the moving plate; and a sensor coil provided on
almost the same plane as the driving coil of the moving plate. In
this case, the driving circuit has a current supplying device for
supplying a current containing at least an alternating-current
component to the driving coil; a detecting device for detecting an
induced electromotive force generated in the sensor coil; a mutual
induction electromotive force generating device for falsely
generating a mutual induction electromotive force caused in the
sensor coil, independent of the driving coil and the sensor coil,
by the current containing at least an alternating-current component
which flows through the driving coil; a subtraction device for
subtracting the output of the mutual induction electromotive force
generating device from the output of the detecting device; and a
control device for controlling the torsional oscillation of the
moving plate in accordance with the output of the subtraction
device.
[0058] According to the present invention constructed as mentioned
above, the mutual induction electromotive force caused in the
sensor coil is falsely generated, independent of the driving coil
and the sensor coil, and the torsional oscillation of the moving
plate is controlled in accordance with the result that the mutual
induction electromotive force falsely generated is subtracted from
the induced electromotive force caused in the sensor coil.
[0059] In order to achieve the above object, the driving circuit
for an optical scanner according to the present invention includes
a support to be fixed to an arbitrary member; a moving plate, at
least one surface of which reflects light; an elastic member
connecting the support and the moving plate; a magnet connected
through the elastic member to the moving plate; a driving coil
provided to the support; and a sensor coil provided to the support.
In this case, the driving circuit has a current supplying device
for supplying a current containing at least an alternating-current
component to the driving coil; a detecting device for detecting an
induced electromotive force generated in the sensor coil; a mutual
induction electromotive force generating device for falsely
generating a mutual induction electromotive force caused in the
sensor coil, independent of the driving coil and the sensor coil,
by the current containing at least an alternating-current component
which flows through the driving coil; a subtraction device for
subtraction-processing the output of the mutual induction
electromotive force generating device from the detecting device;
and a control device for controlling the torsional oscillation of
the moving plate in accordance with the output of the subtraction
device.
[0060] According to the present invention constructed as described
above, the mutual induction electromotive force caused in the
sensor coil is falsely generated, independent of the driving coil
and the sensor coil, and the torsional oscillation of the moving
plate is controlled in accordance with the result that the mutual
induction electromotive force falsely generated is subtracted from
the induced electromotive force caused in the sensor coil.
[0061] Further, in order to achieve the above object, the driving
circuit for an optical scanner according to the present invention
is such that the mutual induction electromotive force generating
device has a first coil and a second coil which are provided on a
fixed substrate; a second current supplying device for supplying a
current containing at least an alternating-current component to the
first coil; and a second detecting device for detecting an induced
electromotive force generated in the second coil. The subtraction
device subtraction-processes the output of the detecting device and
the output of the second detecting device.
[0062] According to the present invention constructed as describe
above, the mutual induction electromotive force caused in the
sensor coil is falsely generated, independent of the driving coil
and the sensor coil, by the first and second coils, the second
current supplying device, and the second detecting device, and the
torsional oscillation of the moving plate is controlled in
accordance with the result that the mutual induction electromotive
force falsely generated is subtracted from the induced
electromotive force caused in the sensor coil.
[0063] Still further, in order to achieve the above object, the
driving circuit for an optical scanner according to the present
invention is such that the mutual induction electromotive force
generating device has a first coil and a second coil which are
provided on the substrate; a second current supplying device for
supplying a current containing at least an alternating-current
component to the first coil; and a second detecting device for
detecting an induced electromotive force generated in the second
coil. The subtraction device subtraction-processes the output of
the detecting device and the output of the second detecting
device.
[0064] According to the present invention constructed as describe
above, the mutual induction electromotive force caused in the
sensor coil is falsely generated, independent of the driving coil
and the sensor coil, by the first and second coils, the second
current supplying device, and the second detecting device, and the
torsional oscillation of the moving plate is controlled in
accordance with the result that the mutual induction electromotive
force falsely generated is subtracted from the induced
electromotive force caused in the sensor coil.
[0065] In the driving circuit for an optical scanner according to
the present invention, it is desirable that the mutual inductance
caused by the driving coil and the sensor coil is practically
equalized to the mutual inductance by the first coil and the second
coil.
[0066] In doing so, a mutual induction electromotive force which is
nearly equal to the mutual induction electromotive force generated
in the sensor coil is generated by the first and second coils, the
second current supplying device, and the second detecting device,
and the torsional oscillation of the moving plate is controlled in
accordance with the result that the mutual induction electromotive
force generated by the first and second coils, the second current
supplying device, and the second detecting device is subtracted
from the induced electromotive force generated in the sensor
coil.
[0067] In the driving circuit for an optical scanner according to
the present invention, it is desirable that the first coil is
configured into nearly the same structure and shape as the driving
coil, the second coil is configured into nearly the same structure
and shape as the sensor coil, the second current supplying device
is constructed similar to the current supplying device, and the
second detecting device is constructed similar to the detecting
device.
[0068] By doing so, a mutual induction electromotive force which is
nearly equal to the mutual induction electromotive force generated
in the sensor coil is generated by the first and second coils, the
second current supplying device, and the second detecting device,
and the torsional oscillation of the moving plate is controlled in
accordance with the result that the mutual induction electromotive
force generated by the first and second coils, the second current
supplying device, and the second detecting device is subtracted
from the induced electromotive force generated in the sensor
coil.
[0069] Further, in order to achieve the above object, the driving
circuit for an optical scanner according to the present invention
has a first gain circuit increasing or decreasing a current to be
supplied through the second current supplying device and a second
gain circuit increasing or decreasing an output with the second
detecting device.
[0070] According to the present invention constructed as mentioned
above, a mutual induction electromotive force which is nearly equal
to the mutual induction electromotive force generated in the sensor
coil is generated by the first and second coils, the second current
supplying device, the second detecting device, and the first and
second gain circuits, and the torsional oscillation of the moving
plate is controlled in accordance with the result that the mutual
induction electromotive force generated by the first and second
coils, the second current supplying device, the second detecting
device, and the first and second gain circuits is subtracted from
the induced electromotive force generated in the sensor coil.
[0071] Still further, in order to achieve the above object, the
driving circuit for an optical scanner according to the present
invention is such that the mutual induction electromotive force
generating device falsely generates the mutual induction
electromotive force caused in the sensor coil, independent of the
driving coil and the sensor coil, in accordance with the current
supplied to the driving coil.
[0072] According to the present invention constructed as mentioned
above, the mutual induction electromotive force caused in the
sensor coil is falsely generated, independent of the driving coil
and the sensor coil, in accordance with the current supplied to the
driving coil, and the torsional oscillation of the moving plate is
controlled in accordance with the result that the mutual induction
electromotive force falsely generated is subtracted from the
induced electromotive force caused in the sensor coil.
[0073] In the driving circuit for an optical scanner according to
the present invention, it is favorable that the mutual induction
electromotive force generating device has a phase shifting device
for shifting the phase of a signal produced in accordance with the
current supplied to the driving coil and a variable gain device for
increasing or decreasing the signal produced in accordance with the
current supplied to the driving coil.
[0074] In doing so, by the mutual induction electromotive force
generating device having the phase shifting device for shifting the
phase of the signal produced in accordance with the current
supplied to the driving coil and the variable gain device for
increasing or decreasing the signal produced in accordance with the
current supplied to the driving coil, the mutual induction
electromotive force caused in the sensor coil is falsely generated,
independent of the driving coil and the sensor coil, and the
torsional oscillation of the moving plate is controlled in
accordance with the result that the mutual induction electromotive
force falsely generated is subtracted from the induced
electromotive force caused in the sensor coil.
[0075] It is favorable that the driving circuit for an optical
scanner according to the present invention is provided with at
least one of an amplitude control device for continuously
controlling the amplitude of the torsional oscillation of the
moving plate in accordance with the result of the subtraction
device and a frequency control device for continuously controlling
the frequency of the torsional oscillation of the moving plate.
[0076] By doing so, at least one of the amplitude and frequency of
the torsional oscillation of the moving plate is controlled by the
control device.
[0077] Subsequently, in order to achieve the third object, the
driving circuit for an optical scanner according to the present
invention includes a support to be fixed to an arbitrary member; a
moving plate, at least one surface of which reflects light; elastic
members connecting the support and the moving plate; magnets
arranged close to the moving plate at preset distances; a driving
coil provided on the moving plate; and a sensor coil provided on
almost the same plane as the driving coil of the moving plate. In
this case, the driving circuit has an oscillation driving device
for supplying a current containing at least an alternating-current
component to the driving coil to execute a torsional oscillation of
the moving plate within a preset angle; an oscillation detecting
device for detecting the induced electromotive force generated in
the sensor coil, provided with an electromotive force detecting
device for outputting a detecting signal corresponding thereto; an
oscillating frequency control device for controlling the frequency
of the torsional oscillation; a first oscillating amplitude control
device for controlling the amplitude of the torsional oscillation
in accordance with the detecting signal output by the oscillation
detecting device; and a second oscillating amplitude control device
for controlling an oscillating condition with each of frequency
components except for that of the torsional oscillation in
accordance with the detecting signal output by the oscillation
detecting device.
[0078] According to the present invention constructed as described
above, the magnets are arranged in the proximity of the moving
plate at preset distances, and the current containing at least an
alternating-current component is supplied to the driving coil
provided on the moving plate. In this way, a force can be generated
in the driving coil provided on the moving plate, and thereby the
moving plate can be torsion-oscillated. The oscillation detecting
device is capable of detecting the oscillating condition of the
moving plate when the electromotive force detecting device detects
the induced electromotive force generated in the sensor coil
provided on the moving plate. The oscillating frequency control
device controls the frequency for torsion-oscillating the moving
plate. The oscillation detecting device detects the oscillating
condition thereof, and in accordance with this detecting signal,
the first oscillating amplitude control device is capable of
controlling the amplitude of the torsional oscillation. In
accordance with the detecting signal, the second oscillating
amplitude control device is capable of controlling the oscillating
condition with each of frequency components except for that of the
torsional oscillation of the moving plate.
[0079] In order to achieve the above object, the driving circuit
for an optical scanner according to the present invention includes
a support to be fixed to an arbitrary member; a moving plate, at
least one surface of which reflects light; an elastic member
connecting the support and the moving plate; a magnet connected
through the elastic member to the moving plate; a driving coil
provided to the support; and a sensor coil provided to the support.
In this case, the driving circuit has an oscillation driving device
for supplying a current containing at least an alternating-current
component to the driving coil to execute a torsional oscillation of
the moving plate within a preset angle; an oscillation detecting
device for detecting the induced electromotive force generated in
the sensor coil, provided with an electromotive force detecting
device for outputting a detecting signal corresponding thereto; an
oscillating frequency control device for controlling the frequency
of the torsional oscillation; a first oscillating amplitude control
device for controlling the amplitude of the torsional oscillation
in accordance with the detecting signal output by the oscillation
detecting device; and a second oscillating amplitude control device
for controlling an oscillating condition with each of frequency
components except for that of the torsional oscillation in
accordance with the detecting signal output by the oscillation
detecting device.
[0080] According to the present invention constructed as mentioned
above, the current containing at least an alternating-current
component is supplied to the driving coil provided to the support.
In this way, forces can be generated in the magnet connected
through the elastic member to the moving plate, and thereby the
moving plate can be torsion-oscillated. The oscillation detecting
device is capable of detecting the oscillating condition of the
moving plate when the electromotive force detecting device detects
the induced electromotive force generated in the sensor coil
provided to the support.
[0081] In the present invention, it is desirable that the second
oscillating amplitude control device has a low-pass filter for
extracting a frequency component lower than the frequency of the
torsional oscillation from the detecting signal and a low-frequency
oscillation eliminating device for controlling the oscillating
condition of the moving plate so that its output becomes zero.
[0082] When the present invention is constructed as described
above, the low-pass filter extracts an oscillating motion with a
lower frequency than in the torsional oscillation of the moving
plate, and the low-frequency oscillation eliminating device makes
control so that the output of the low-pass filter becomes zero.
Consequently, the oscillating motion with a lower frequency than in
the torsional oscillation of the moving plate can be
eliminated.
[0083] In the present invention, it is desirable that the
oscillating frequency control device is provided with a resonant
frequency follow-up control device for executing the torsional
oscillation of the moving plate at the mechanical resonant
frequency in accordance with the detecting signal.
[0084] By doing so, the moving plate can be continuously
torsion-oscillated at the mechanical resonant frequency.
[0085] Subsequently, in order to achieve the fourth object, the
driving circuit for an optical scanner according to the present
invention includes a support to be fixed to an arbitrary member; a
moving plate, at least one surface of which reflects light; elastic
members connecting the support and the moving plate; magnets
arranged close to the moving plate at preset distances; a driving
coil provided on the moving plate; and a sensor coil provided on
the moving plate. In this case, the driving circuit has an
oscillation driving device for supplying a current containing at
least an alternating-current component to the driving coil to
execute the torsional oscillation of the moving plate within a
preset angle; an oscillation detecting device for detecting the
oscillating condition of the moving plate in accordance with the
induced electromotive force generated in the sensor coil; an
amplitude control device for controlling the amplitude of the
oscillation of the moving plate in accordance with the output of
the oscillation detecting device; and a frequency control device
for controlling the oscillating frequency of the moving plate. The
oscillation detecting device has a constant-voltage source
connected in series to the sensor coil; a voltage detecting device
for detecting voltages created at both terminals of a series
circuit comprised of the sensor coil and the constant-voltage
source to output signals corresponding thereto; a constant-voltage
eliminating device for outputting a signal in which a
constant-voltage component is eliminated from the output of the
voltage detecting device; and a constant-voltage extracting device
for extracting the constant-voltage component from the output of
the voltage detecting device to output a signal corresponding
thereto.
[0086] According to the present invention constructed as described
above, in the oscillation driving device, the magnets are arranged
in the proximity of the moving plate at preset distances, and the
current containing at least an alternating-current component is
supplied to the driving coil provided on the moving plate. In this
way, a force can be generated in the driving coil provide on the
moving plate, and thereby the moving plate is torsion-oscillated.
The oscillation detecting device detects the oscillating condition
of the moving plate when the electromotive force detecting device
detects the induced electromotive force generated in the sensor
coil provided on the moving plate. The amplitude control device
controls the oscillating amplitude of the moving plate in
accordance with the output of the oscillation detecting device. The
frequency control device controls the oscillating frequency of the
moving plate. In the oscillation detecting device, the voltage
detecting device detects the voltages at both terminals of the
series circuit comprised of the sensor coil and the
constant-voltage source to produce the signal in which the
constant-voltage component is eliminated from the result of the
detection. Moreover, in the oscillation detecting device, the
constant-voltage component is extracted from the output of the
voltage detecting device. Since the constant-voltage component
obtained here is to indicate the resistance value of the sensor
coil, it is possible to know the influence of the fluctuation of
the resistance value of the sensor coil on the oscillating
condition of the optical scanner.
[0087] Further, in order to achieve the above object, the driving
circuit for an optical scanner includes a support to be fixed to an
arbitrary member; a moving plate, at least one surface of which
reflects light; an elastic member connecting the support and the
moving plate; a magnet connected through the elastic member to the
moving plate; a driving coil provided to the support; and a sensor
coil provided to the support. In this case, the driving circuit has
an oscillation driving device for supplying a current containing at
least an alternating-current component to the driving coil to
execute a torsional oscillation of the moving plate within a preset
angle; an oscillation detecting device for detecting the
oscillating condition of the moving plate in accordance with the
induced electromotive force generated in the sensor coil; an
amplitude control device for controlling the amplitude of the
oscillation of the moving plate in accordance with the output of
the oscillation detecting device; and a frequency control device
for controlling the oscillating frequency of the moving plate. The
oscillation detecting device has a constant-voltage source
connected in series to the sensor coil; a voltage detecting device
for detecting voltages created at both terminals of a series
circuit comprised of the sensor coil and the constant-voltage
source to output signals corresponding thereto; a constant-voltage
eliminating device for outputting a signal in which a
constant-voltage component is eliminated from the output of the
voltage detecting device; and a constant-voltage extracting device
for extracting the constant-voltage component from the output of
the voltage detecting device to output a signal corresponding
thereto.
[0088] According to the present invention constructed as mentioned
above, the oscillation driving device is such that the current
containing at least an alternating-current component is supplied to
the driving coil provided to the support to thereby generate the
forces in the magnet connected through the elastic member to the
moving plate. Consequently, the moving plate is torsion-oscillated.
In the oscillation detecting device, the electromotive force
detecting device detects the induced electromotive force caused in
the sensor coil provided to the support, thereby detecting the
oscillating condition of the moving plate. The amplitude control
device controls the amplitude of the oscillation of the moving
plate in accordance with the output of the oscillation detecting
device. The frequency control device controls the oscillating
frequency of the moving plate. Further, in the oscillation
detecting device, the voltage detecting device detects voltages at
both terminals of the series circuit composed of the sensor coil
and the constant-voltage source to produce the signal in which the
constant-voltage component is eliminated from the result of the
detection. Still further, in the oscillation detecting device, the
constant-voltage component is extracted from the output of the
voltage detecting device. Since the constant-voltage component
obtained here is to indicate the resistance value of the sensor
coil, it is possible to know the influence of the fluctuation of
the resistance value of the sensor coil on the oscillating
condition of the optical scanner.
[0089] Still further, in order to achieve the above object, the
driving circuit for an optical scanner according to the present
invention, in addition to the above construction of the driving
circuit for an optical scanner, is such that the oscillation
detecting device is provided with a division device for dividing
the output of the constant-voltage eliminating device by the output
of the constant-voltage extracting device.
[0090] According to the present invention constructed as mentioned
above, "the signal in which the constant-voltage component is
eliminated" obtained by the oscillation detecting device can be
divided by "the constant-voltage component" obtained by the
oscillation detecting device. Consequently, the oscillating
condition of the optical scanner can be found in which the
influence of the fluctuation of the resistance value of the sensor
coil is excluded.
[0091] These and other objects as well as the features and
advantages of the present invention will become apparent from the
following description of the preferred embodiments when taken in
conjunction with the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0092] FIG. 1 is a schematic view for illustrating an operating
principle of the optical scanner;
[0093] FIG. 2A is a graph showing characteristics of the
oscillating angle relative to the oscillating frequency of the
optical scanner;
[0094] FIG. 2B is a graph showing characteristics of the phase
relative to the oscillating frequency of the optical scanner;
[0095] FIG. 3 is a view showing a schematic structure of the
optical scanner to which the driving circuit of the present
invention is applied;
[0096] FIG. 4A is a diagram showing the waveform of a driving
signal in a resonant frequency drive;
[0097] FIG. 4B is a diagram showing the oscillating waveform of the
optical scanner in the resonant frequency drive;
[0098] FIG. 4C is a diagram showing the oscillating waveform of a
sensor signal (the electromotive force of a sensor coil) in the
resonant frequency drive;
[0099] FIG. 5 is a block diagram showing a schematic construction
of circuitry for control-driving the optical scanner according to
the present invention;
[0100] FIG. 6 is a diagram showing an example of the configurations
of a driving circuit and a detecting circuit in the circuitry of
FIG. 5;
[0101] FIG. 7 is a view for illustrating a state where the driving
signal is delivered to the driving coil of the optical scanner in
FIG. 3;
[0102] FIG. 8A is a diagram showing the waveform of the driving
signal in the resonant frequency drive;
[0103] FIG. 8B is a diagram showing the waveform of a mutual
induction electromotive force in a resonant frequency drive;
[0104] FIG. 8C is a diagram showing the waveform of a true
electromotive force (the sensor signal) in a resonant frequency
drive;
[0105] FIG. 9A is a graph showing a state where an
amplitude-modulation noise is produced with respect to the
oscillating motion of the optical scanner;
[0106] FIG. 9B is a graph showing a state where the center of
oscillation fluctuates with respect to the oscillating motion of
the optical scanner;
[0107] FIG. 9C is a graph showing an actual oscillating state of
the optical scanner where the oscillations of FIGS. 9A and 9B are
superimposed;
[0108] FIG. 10 is a diagram showing another example of the
configuration of the detecting circuit in the circuitry of FIG.
5;
[0109] FIG. 11 is a diagram showing still another example of the
configuration of the detecting circuit in the circuitry of FIG.
5;
[0110] FIG. 12 is a view showing the construction of a control
circuit used in a first embodiment of the present invention;
[0111] FIG. 13 is a graph showing an example of characteristics of
the gain relative to the frequency in an integrating circuit of the
control circuit of FIG. 12;
[0112] FIG. 14 is a graph showing another example of
characteristics of the gain relative to the frequency in an
integrating circuit of the control circuit of FIG. 12;
[0113] FIG. 15 is a view showing the construction of a control
circuit used in a second embodiment of the present invention;
[0114] FIG. 16 is a block diagram showing a schematic construction
of a third embodiment of the present invention;
[0115] FIG. 17 is a view showing a schematic structure of a dummy
scanner used in the third embodiment;
[0116] FIG. 18 is a diagram showing an example of the
configurations of a dummy driving circuit and a dummy detecting
circuit, used in the third embodiment;
[0117] FIG. 19 is a block diagram showing an example of the
construction of a control circuit used in the third embodiment;
[0118] FIG. 20 is a block diagram showing another example of the
construction of a control circuit used in the third embodiment;
[0119] FIG. 21 is a block diagram showing a schematic construction
of a fourth embodiment of the present invention;
[0120] FIG. 22 is a block diagram showing a schematic construction
of a fifth embodiment of the present invention;
[0121] FIG. 23 is a block diagram showing a schematic construction
of a mutual induction component producing circuit used in the fifth
embodiment;
[0122] FIG. 24 is a view showing a schematic structure of another
example of the optical scanner to which the driving circuit of the
present invention is applied;
[0123] FIG. 25 is a view showing a schematic structure of still
another example of the optical scanner to which the driving circuit
of the present invention is applied;
[0124] FIG. 26 is a view showing the construction of a control
circuit used in a sixth embodiment of the present invention;
[0125] FIG. 27 is a view showing the construction of a control
circuit used in a seventh embodiment of the present invention;
[0126] FIG. 28A is a graph showing gain characteristics where a PI
circuit in FIGS. 26 and 27 is constructed with a P control circuit
(proportional circuit) and an I control circuit (integrating
circuit);
[0127] FIG. 28B is a graph showing gain characteristics where the
PI circuit in FIGS. 26 and 27 is constructed with the P control
circuit (proportional circuit), the I control circuit (integrating
circuit), and a D control circuit (differentiating circuit);
[0128] FIG. 29 is a diagram showing the configuration of a driving
circuit used in an eighth embodiment of the present invention;
and
[0129] FIG. 30 is a diagram showing the configuration of a driving
circuit used in a ninth embodiment of the present invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0130] The embodiments of the driving circuit for an optical
scanner of the present invention will be described below.
[0131] First Embodiment
[0132] The optical scanner 1 to which the driving circuit of the
present invention is applied, as shown in FIG. 3, includes the
mirror portion 101 in which the coil pattern (the driving coil 102)
and the sensor coil 103 are provided parallel with the mirror face
101a; the spring portions 104a and 104b for oscillating the mirror
portion 101; and the permanent magnets 105a and 105b arranged close
to the mirror portion 101, for producing the magnetic field nearly
parallel with the mirror face 101a where the mirror portion 101 is
in a stationary state. The spring portions 104a and 104b are
connected to a support, not shown, to be fixed to an arbitrary
member. By supplying the alternating current (of the frequency f)
to the driving coil 102, a force obeying the left-hand rule is
generated in a direction normal to the mirror face 101a to
oscillate the mirror portion 101 at the frequency f.
[0133] FIG. 5 shows the circuitry for control-driving the optical
scanner 1 to which the driving circuit of the present invention is
applied. In the circuitry of FIG. 5, from the operating controller
such as a PC, not shown, a control signal which commands the
desired driving condition of the optical scanner 1, such as the
oscillating amplitude (oscillating angle) or oscillating frequency
of the optical scanner 1, is supplied to the control circuit 4. The
control circuit 4, when receiving the control signal, outputs the
driving command signal V.sub.d to the driving circuit 2. The
driving circuit 2 outputs the driving signal (the alternating
current) to the driving coil 102 in accordance with the driving
command signal V.sub.d. The optical scanner 1 is thus oscillated at
desired oscillating angle and oscillating frequency. In this case,
at both ends of the sensor coil 103, the sensor coil 103 is
interlinked with the magnetic field produced by the permanent
magnets 105a and 105b and thereby the electromotive force (the
sensor signal) is generated. This electromotive force (the sensor
signal) is feedbacked to the control circuit 4 as the detecting
signal V.sub.s detected by the detecting circuit 3. In the control
circuit 4, the detecting signal V.sub.s is monitored so that when
the oscillating amplitude (the oscillating angle) or oscillating
frequency of the optical scanner 1 is out of a desired value, the
driving command signal V.sub.d output to the driving circuit 2 is
compensated. In this way, the optical scanner 1 can be controlled
and driven with stability.
[0134] Subsequently, the constructions of the driving circuit 2,
the detecting circuit 3-a, and a control circuit 4a, as an example
for each, are shown in FIGS. 6 and 12. As shown in FIG. 6, the
driving circuit 2 includes the operational amplifier 201 and the
resistance element (R0) 202 so that they convert the driving
command signal V.sub.d into the driving signal (the alternating
current).
[0135] Here, when the driving signal supplied to the driving coil
102 is expressed as I=I.sub.0 sin(2.pi.ft), the relation between
the driving command signal V.sub.d and the driving signal (the
alternating current) is given by the following equation:
V.sub.d=R.sub.0.multidot.I=R.sub.0.multidot.I.sub.0.multidot.sin(2.pi.ft)
(18)
[0136] The detecting circuit 3-a includes the operational amplifier
301, the resistance element (R1) 302, the resistance element (R1)
303, the resistance element (R2) 304, and the resistance element
(R2) 305 so that they convert the electromotive force (the sensor
signal) into the detecting signal V.sub.s.
[0137] Here, again, when the electromotive force is denoted by
V.sub.r, the resistance value of the sensor coil is denoted by
R.sub.sens, and the self-inductance and wiring capacity of the
sensor coil 103 are assumed to be negligible, the relation between
the electromotive force V.sub.r and the detecting signal V.sub.s is
given by the following equation: 11 V s = - 2 R 2 2 R 1 + R sens V
r ( 19 )
[0138] FIG. 12 is block diagram showing the first embodiment (the
control circuit 4a) of the control circuit 4 which controls the
oscillating amplitude and oscillating frequency of the optical
scanner 1 in accordance with the detecting signal V.sub.s output
from the detecting circuit 3. The great advantage of the present
invention lies in the circuit configuration of the control circuit
4.
[0139] The control circuit 4a is adapted to construct a positive
feedback loop with an amplifier circuit 403, a filter circuit 404,
a phase-shifting circuit 408, and a gain control circuit 402, and
thereby has a function (a resonant frequency follow-up control
function) of oscillating the optical scanner 1 at the mechanical
resonant frequency f.sub.c.
[0140] Furthermore, the control circuit 4a is adapted to construct
a negative feedback loop with the amplifier circuit 403, the filter
circuit 404, an integrating circuit 409, an amplitude detecting
circuit 405, a subtraction circuit 406, a PI circuit 407, and the
gain control circuit 402, and thereby has a function (an
oscillating amplitude control function) of oscillating the optical
scanner 1 at a desired oscillating amplitude (oscillating
angle).
[0141] The amplifier circuit 403 is designed to increase the
amplitude at a preset factor in order to facilitate the control of
the signal level (signal amplitude) of the detecting signal
V.sub.s.
[0142] The filter circuit 404 is constructed with a band-pass
filter which extracts only the oscillating frequency component (the
frequency component indicated by a frequency command value) and
plays a role of noise elimination. Also, although it is most
desirable that the filter circuit 404 is constructed with the
band-pass filter, the same effect is brought about even when a
low-pass filter or high-pass filter is used or the filter is not
used, depending on the condition of noise.
[0143] The phase-shifting circuit 408 is designed to make phase
adjustment so that the driving command signal V.sub.d output from
the gain control circuit 402 agrees in phase with the detecting
signal V.sub.s supplied to the amplifier circuit 403 (because both
signals agree in phase with each other in the oscillation at the
resonant frequency), and is constructed so that the signal is
delivered to gain control circuit 402 by shifting the phase of the
output of the filter circuit 404. Also, the amount of phase
adjustment made here is governed by the amount of phase shift at
each of the amplifier circuit 403, the filter circuit 404, and the
gain control circuit 402. The gain control circuit 402 is
constructed to control the amplitude of the signal supplied from
the phase-shifting circuit 408 in accordance with the control
signal output from the PI circuit 407 and to output the driving
command signal V.sub.d.
[0144] The integrating circuit 409 is adapted to apply the gain of
the reciprocal of the frequency (k/f, where k is a constant) to the
output of the filter circuit 404. Here, it is desirable that the
constant k is set to a resonant frequency f.sub.co of the optical
scanner in the initial condition. (Also, the initial condition
refers to a condition where the influence of a change of ambience
or a change with age is zero.)
[0145] Since in the integrating circuit 409 the gain of the
reciprocal of the frequency (k/f, where k is a constant) is applied
to the output of the filter circuit 404, the gain is increased
unlimitedly in a low-frequency region, notably a DC
(zero-frequency) region, and a low-frequency noise, such as a
source noise, is increased.
[0146] Thus, in the first embodiment, the integrating circuit is
constructed to have a gain characteristic of the reciprocal of the
frequency (k/f, where k is a constant) only in the frequency band
close to the resonant frequency of the optical scanner 1 in the
initial condition (at least, the width of shift of the resonant
frequency which fluctuates due to a change of ambience or a change
with age).
[0147] Specifically, when the integrating circuit 409, as shown in
FIG. 13, is constructed with a low-pass filter of .times.10 gain
which has a cutoff frequency (400 Hz) equal to {fraction (1/10)} of
the resonant frequency f.sub.co (assumed to be 4000 Hz) of the
optical scanner 1 in the initial condition, the gain becomes
.times.1 at the resonant frequency f.sub.co and thus is easy to
handle, and the design is facilitated. With such gain
characteristics, the gain becomes the reciprocal of the frequency
in a band close to the resonant frequency f.sub.co, and a flat gain
characteristic is obtained in the low-frequency region. Therefore,
an effect is produced on the above problem. Alternatively, when the
integrating circuit 409 is constructed by a combination of the
low-pass filter with the characteristics shown in FIG. 13 and a
high-pass filter of .times.1 gain which has a cutoff frequency 400
Hz as shown in FIG. 14, an effect is brought about on noise
elimination in the low-frequency region.
[0148] The amplitude detecting circuit 405 is designed to detect an
amplitude value (or an RMS value) of the supplied signal so that a
resulting detecting signal is output to the subtraction circuit
406. The subtraction circuit 406 is adapted to find a deviation
between an amplitude value obtained by the amplitude detecting
circuit 405 and an amplitude command value which is the control
signal so that a resulting deviation signal is output to the PI
circuit 407. The PI circuit 407 has an I circuit (an integrating
circuit) an a P circuit (a proportional circuit) so that the
deviation signal output from the subtraction circuit 406 is
amplified by a preset gain and a resulting control signal is output
to the gain control circuit 402.
[0149] Subsequently, a description is given of the operation of the
control driving circuit of the optical scanner, shown in FIGS. 3,
5, 6, and 12.
[0150] In the initial condition where the optical scanner 1 is not
oscillated, since the output V.sub.s of the detecting circuit 3 is
zero and the amplitude command value of the control signal is
supplied to the subtraction circuit 406, the output of the
subtraction circuit 406 becomes plus and the control signal
produced in the PI circuit 407 is increased (a negative feedback
gain becomes at least 1). As a result, the optical scanner 1 starts
the oscillation at the resonant frequency, and the gain control
circuit 402 is operated to increase the oscillating amplitude of
the optical scanner 1 until the output V.sub.s of the detecting
circuit 3-a agrees with the amplitude command value (until the
output of the subtraction circuit 406 becomes zero).
[0151] Conversely, where the output V.sub.s of the detecting
circuit 3-a exceeds the amplitude command value, the gain control
circuit 402 is operated to decrease the amplitude of a sine wave (a
rectangular wave or pulse wave) signal output from the
phase-shifting circuit 408 and to decrease the oscillating
amplitude of the optical scanner 1.
[0152] In the control circuit 4a, the optical scanner can thus be
always driven at the resonant frequency and even when the resonant
frequency fluctuates, the amplitude can be controlled with a high
degree of accuracy.
[0153] Also, although the first embodiment brings about an effect
where the optical scanner is driven at the resonant frequency, the
present invention is also effective where it is driven at an
arbitrary frequency (where the resonant frequency follow-up control
is not made). Thus, a construction in this case is described as the
second embodiment.
[0154] Second Embodiment
[0155] FIG. 15 is a block diagram showing the second embodiment (a
control circuit 4b) of the control circuit 4 used in the driving
circuit for an optical scanner of the present invention.
[0156] The control circuit 4b of the second embodiment has the same
construction as the control circuit 4a of the first embodiment with
the exception that an oscillating circuit 401 connected to an
operating controller, not shown, is provided instead of the
phase-shifting circuit 408 connected to the filter circuit 404 in
the first embodiment of FIG. 12. In the second embodiment, as shown
in FIG. 15, the control signal includes two command values, the
frequency command value and the amplitude command value, and the
frequency command value is first supplied to the oscillating
circuit 401. In the oscillating circuit 401, a sine-wave signal
with a preset amplitude at a frequency indicated by the frequency
command value, or a rectangular wave (a pulse wave) including a
sine-wave component, is produced and is output to the gain control
circuit 402. In the gain control circuit 402, the amplitude of the
sine-wave signal (or the sine-wave component) output from the
oscillating circuit 401 is controlled in accordance with the
control signal output from the PI circuit 407, and the driving
command signal V.sub.d is output. The construction of the negative
feedback loop controlling the amplitude is the same as in the first
embodiment, and thus its explanation is omitted.
[0157] Also, in the control circuit 4a of the first embodiment, as
describe above, it is favorable that the integrating circuit 409 is
constructed with the filter of the gain characteristic of k/f in
the frequency band close to the resonant frequency as shown in FIG.
13 or 14. In the control circuit 4b of the second embodiment,
however, it is necessary that the integrating circuit 409 is
constructed with a filter of the gain characteristic of k/f in the
range of the frequency command value (the frequency band).
[0158] Here, reference is made to the operation of the control
driving circuit of the optical scanner using the control circuit 4b
constructed as mentioned above.
[0159] In the initial condition where the optical scanner is not
oscillated, when the frequency command value of the control signal
is output, the oscillating circuit 401 outputs the driving command
signal. The driving command value output is supplied through the
gain control circuit 402 to the driving circuit 2. In the initial
condition, since the output V.sub.s of the detecting circuit 3 is
zero and the amplitude command value of the control signal is
supplied to the subtraction circuit 406, the output of the
subtraction circuit 406 becomes plus and the control signal
produced in the PI circuit 407 is increased (a negative feedback
gain becomes at least 1). As a result, the optical scanner 1 starts
the oscillation at a frequency indicated by the frequency command
value, and the gain control circuit 402 is operated to increase the
oscillating amplitude of the optical scanner 1 until the output
V.sub.s of the detecting circuit 3 agrees with the amplitude
command value (until the output of the subtraction circuit 406
becomes zero).
[0160] Conversely, where the output V.sub.s of the detecting
circuit 3 exceeds the amplitude command value, the gain control
circuit 402 is operated to decrease the amplitude of a sine wave (a
rectangular wave or pulse wave) signal output from the oscillating
circuit 401 and to decrease the oscillating amplitude of the
optical scanner 1.
[0161] In the control circuit 4b, the optical scanner can thus be
driven at an arbitrary frequency and the amplitude can be
controlled with a high degree of accuracy.
[0162] According to the present invention, as will be obvious from
the above description, the influence of a change of the driving
frequency on the optical scanner can be eliminated, and
high-precision amplitude control becomes possible. As a result, the
driving circuit for an optical scanner in which an optical scan
with permanent stability is possible can be provided.
[0163] Third Embodiment
[0164] FIG. 16 shows a schematic construction of the third
embodiment in the driving circuit for an optical scanner according
to the present invention.
[0165] In addition to the construction of the driving circuit for
an optical scanner shown in FIG. 5, the driving circuit for an
optical scanner of the third embodiment has a dummy driving circuit
6 driving a dummy scanner 5, a dummy detecting circuit 7 detecting
the driving condition of the dummy scanner 5, and a subtraction
circuit 8.
[0166] The optical scanner 1, the driving circuit 2, and the
detecting circuit 3 are constructed to be almost identical with
those described with reference to FIGS. 2A, 2B, 4A, and 4B.
[0167] The dummy scanner 5, as illustrated in FIG. 17, has a
substrate 501, a dummy driving coil 502, and a dummy sensor coil
503. Although it is desirable that the dummy scanner 5 is identical
in shape and structure in the manufacturing process with a moving
plate section (constructed with the mirror portion 101, the driving
coil 102, the sensor coil 103, and the spring portions 104a and
104b) of the optical scanner 1, it is only necessary to at least
meet the conditions described below.
[0168] The substrate 501, like a common electric circuit substrate,
must be constructed of an electric insulator, and the mutual
inductance with the mutual induction function of the dummy driving
coil 502 and the dummy sensor coil 503 must be identical with that
of the driving coil 102 and the sensor coil 103.
[0169] However, the dummy scanner 5, unlike the optical scanner 1
in FIG. 3, is not provided with permanent magnets corresponding to
the two permanent magnets 105a and 105b arranged close to the
mirror portion 101, for producing a magnetic field nearly parallel
with the mirror face 101a where the mirror portion 101 is in a
stationary state.
[0170] The dummy driving circuit 6 is adapted to supply the current
to the dummy driving coil 502 and, as shown in FIG. 18, includes an
operational amplifier 601 and a resistance element (R0) 602.
[0171] The operational amplifier 601 and the resistance element
(R0) 602 are constructed to be identical with the operational
amplifier 201 and the resistance element (R0) 202, respectively, of
the driving circuit 2 in FIG. 6. Thus, when the same driving
command signal V.sub.d as in the driving circuit 2 is input into
the dummy driving circuit 6 of FIG. 18, the dummy driving circuit 6
sends the driving signal (the alternating current) identical with
that supplied to the driving coil 102 by the driving coil 2 to the
dummy driving coil 502.
[0172] The dummy detecting circuit 7 is adapted to detect the
electromotive force generated in the dummy sensor coil 503 and, as
shown in FIG. 18, includes an operational amplifier 701, a
resistance element (R1) 702, a resistance element (R1) 703, a
resistance element (R2) 704, and a resistance element (R2) 705.
[0173] These are constructed to be identical with the operational
amplifier 301, the resistance element (R1) 302, the resistance
element (R1) 303, the resistance element (R2) 304, and the
resistance element (R2) 305, respectively, of the detecting circuit
3-a in FIG. 6. Therefore, when the electromotive force identical
with that generated in the sensor coil 103 is caused in the dummy
sensor coil 503, the dummy detecting circuit 7 outputs the
detecting signal identical with that output by the detecting
circuit 3.
[0174] The subtraction circuit 8 shown in FIG. 16 is designed to
subtract the output of the dummy detecting circuit 7 from the
output of the detecting circuit 3.
[0175] The control circuit 4 is adapted to control the oscillating
amplitude and frequency of the optical scanner 1 in accordance with
the output of the subtraction circuit 8 (its details will be
described later).
[0176] Subsequently, reference is made to the flow of the signal in
the circuit block diagram shown in FIG. 16.
[0177] From the operating controller such as a PC, not shown, the
control signal which is the command value of a desired driving
condition of the optical scanner 1, such as the oscillating
amplitude (the oscillating angle) or oscillating frequency of the
optical scanner 1, is supplied to the control circuit 4. The
control circuit 4 receives the control signal to output the driving
command signal V.sub.d to the driving circuit 2. The driving
circuit 2 sends the driving signal (the alternating current) to the
driving coil 102 in accordance with the driving command signal
V.sub.d. The optical scanner 1 is thus oscillated at desired
oscillating angle and oscillating frequency. In this case, at both
ends of the sensor coil 103, the sensor coil 103 is interlinked
with the magnetic field produced by the permanent magnets 105a and
105b and the electromotive force generated thereby is induced.
Furthermore, at both ends of the sensor coil 103, the mutual
induction electromotive force generated by supplying the
alternating current to the driving coil 102 is induced. Such
electromotive forces are changed by the detecting circuit 3 into
the detecting signal V.sub.s, which is output to the subtraction
circuit 8.
[0178] The control circuit 4, on the other hand, sends the same
signal as the driving command signal V.sub.d supplied to the
driving circuit 2, to the dummy driving circuit 6 as well. The
dummy driving circuit 6 sends the same signal as the driving signal
(the alternating current) supplied to the driving coil 102 by the
driving circuit 2, to the dummy driving coil 502 as well, in
accordance with the driving command signal V.sub.d. In this case,
at both ends of the dummy sensor coil 503, only the mutual
induction electromotive force generated by supplying the
alternating current to the dummy driving coil 502 is induced. This
mutual induction electromotive force e.sub.r is the same as that
generated at both ends of the sensor coil 103. The mutual induction
electromotive force e.sub.r is changed by the dummy detecting
circuit 7 into a detecting signal V.sub.n, which is output to the
subtraction circuit 8.
[0179] In the subtraction circuit 8, the detecting signal V.sub.n
output by the dummy detecting circuit 7 is subtracted from the
detecting signal V.sub.s output by the detecting circuit 3, and a
resulting signal V.sub.s-n is supplied to the control circuit 4.
This signal V.sub.s-n exhibits only the electromotive force
generated when the sensor coil 103 is interlinked with the magnetic
field produced by the permanent magnets 105a and 105. The result is
that the mutual induction electromotive force e.sub.r responsible
for hindrance to the control of the optical scanner 1 with a high
degree of accuracy can be eliminated.
[0180] In the control circuit 4, the subtraction signal V.sub.s-n
is monitored so that when the oscillating amplitude (the
oscillating angle) or oscillating frequency of the optical scanner
1 is out of a desired value, the driving command signal V.sub.d is
compensated. In this way, the optical scanner 1 can be controlled
with a high degree of accuracy.
[0181] Subsequently, the control circuit 4 will be specifically
described.
[0182] FIG. 19 shows the construction of a control circuit 4c which
is an example of the control circuit 4. In the control circuit 4a,
the control signal includes two command values, the frequency
command value and the amplitude command value, and the frequency
command value is first supplied to the oscillating circuit 401. In
the oscillating circuit 401, a sine-wave signal with a preset
amplitude at a frequency indicated by the frequency command value,
or a rectangular wave (a pulse wave) including a sine-wave
component, is produced and is output to the gain control circuit
402. In the gain control circuit 402, the amplitude of the
sine-wave signal (or the sine-wave component) output from the
oscillating circuit 401 is controlled in accordance with the
control signal output from the PI circuit 407, and the driving
command signal V.sub.d is output.
[0183] On the other hand, when the signal V.sub.s-n output from the
subtraction circuit 8 is delivered to the amplifier circuit 403,
the amplitude of the signal V.sub.s-n is increased at a preset
factor in the amplifier circuit 403 in order to facilitate the
control of the amplitude, and this signal is output to the filter
circuit 404.
[0184] The filter circuit 404 is constructed with a band-pass
filter which extracts only the oscillating frequency component (the
frequency component indicated by a frequency command value) and
plays a role of noise elimination. Also, although it is most
desirable that the filter circuit 404 is constructed with the
band-pass filter, the same effect is brought about even when a
low-pass filter or high-pass filter is used or the filter is not
used, depending on the condition of noise. Also, even though the
order of the amplifier circuit 403 and the filter circuit 404 is
reversed, the same role can be played.
[0185] The signal V.sub.s-n in which the noise is eliminated by the
filter circuit 404 is supplied to the amplitude detecting circuit
405.
[0186] The amplitude detecting circuit 405 is designed to detect an
amplitude value (or an RMS value) of the signal V.sub.s-n so that a
resulting detecting signal is output to the subtraction circuit
406. The subtraction circuit 406 is designed to find a deviation
between the amplitude value of the signal V.sub.s-n to be supplied
and the amplitude command value of another control signal so that a
resulting deviation signal is output to the PI circuit 407. The PI
circuit 407 has an I circuit (an integrating circuit) an a P
circuit (a proportional circuit) so that the deviation signal is
amplified by a preset gain in accordance with the frequency
component of the deviation signal output from the subtraction
circuit 406 and a resulting control signal is output to the gain
control circuit 402.
[0187] Subsequently, the operation of the control circuit 4c will
be explained.
[0188] In the initial condition where the optical scanner 1 is not
oscillated, when the frequency command value (which is here thought
of as the resonant frequency) of the control signal is output, the
oscillating circuit 401 outputs the driving command signal. The
driving command value output is supplied through the gain control
circuit 402 to the driving circuit 2. In the initial condition,
since the signal V.sub.s-n is zero and the amplitude command value
of the second control signal is supplied to the subtraction circuit
406, the output of the subtraction circuit 406 becomes plus and the
control signal produced in the PI circuit 407 is increased. Hence,
the gain control circuit 402 is operated to increase the amplitude
of the driving common signal. In this way, the optical scanner 1
starts the oscillation at a frequency indicated by the control
signal (the frequency command value). An amplitude control section
including the PI circuit 407 and the gain control circuit 402 is
operated to increase the amplitude of the driving command signal
V.sub.d until the output of the subtraction circuit 406 becomes
zero, namely until the output signal V.sub.s-n from the subtraction
circuit 8 agrees with the amplitude command value.
[0189] Conversely, where the signal V.sub.s-n exceeds the amplitude
command value, the output of the subtraction circuit 406 becomes
minus and the amplitude control section including the PI circuit
407 and the gain control circuit 402 is operated to decrease the
amplitude of the driving command signal V.sub.d.
[0190] In the control circuit 4c, the oscillating amplitude of the
optical scanner 1 can thus be controlled to maintain a preset
value.
[0191] FIG. 20 shows the construction of a control circuit 4d which
is another example of the control circuit 4.
[0192] In FIG. 20, the control circuit 4d has the same construction
as the control circuit 4c with the exception that the
phase-shifting circuit 408 connecting to the filter circuit 404 is
provided instead of the oscillating circuit 401 connected to the
operating controller, not shown, in the control circuit 4c of FIG.
19.
[0193] In the control circuit 4d, the gain control circuit 402, the
amplifier circuit 403, the filter circuit 404, the amplitude
detecting circuit 405, the subtraction circuit 406, and the PI
circuit 407 are constructed to have the same functions as those in
the control circuit 4c of FIG. 16.
[0194] The phase-shifting circuit 408 is adapted to make phase
adjustment so that the driving command signal V.sub.d output from
the gain control circuit 402 agrees in phase with the signal
V.sub.s-n supplied to the amplifier circuit 403 (because both
signals agree in phase with each other in the oscillation at the
resonant frequency), and is constructed so that the signal is
delivered to gain control circuit 402 by shifting the phase of the
output of the filter circuit 404. Also, the amount of phase
adjustment made here is governed by the amount of phase shift at
each of the amplifier circuit 403, the filter circuit 404, and the
gain control circuit 402.
[0195] In the control circuit 4d constructed as mentioned above,
the positive feedback loop is constructed with an amplifier circuit
403, a filter circuit 404, a phase-shifting circuit 408, and a gain
control circuit 402. In the initial condition, as in the control
circuit 4c of FIG. 19, the gain of the negative feedback loop
becomes at least 1 due to the amplitude control section including
the PI circuit 407 and the gain control circuit 402, and hence the
oscillation is started. That is, the optical scanner 1 is
oscillated at the resonant frequency and, at the same time, the
oscillating amplitude is controlled by the amplitude control
section.
[0196] In this way, in the control circuit 4d, the oscillating
frequency of the optical scanner 1 is controlled to follow up the
mechanical resonant frequency, and the oscillating amplitude can be
controlled to maintain the preset value.
[0197] According to the driving circuit for an optical scanner of
the third embodiment, therefore, the optical scanner 1 can be
controlled in regard to the amplitude or the amplitude and
frequency with a high degree of accuracy.
[0198] In the driving circuit for an optical scanner of the third
embodiment of the present invention, however, the following two
problems remain.
[0199] First, the optical scanner mentioned above, including the
conventional one, is driven by the current and thus tends to
increase power consumption. In the case of the optical scanner
using the driving circuit for an optical scanner of the first
embodiment, a twofold power is consumed due to the currents flowing
through the optical scanner and the dummy scanner.
[0200] Second, in the case of a microscanner fabricated by using
the semiconductor process, driving efficiency is favorable and
power consumption is lessened. However, the mutual induction
electromotive force is also lessened, and it becomes difficult that
the dummy scanner is used to eliminate the mutual induction
electromotive force with a high degree of accuracy.
[0201] Subsequently, a description will be given of the driving
circuit for an optical scanner according to the fourth embodiment
of the present invention which is configured for the purpose of
lowering the power consumption or improving the S/N ratio.
[0202] Fourth Embodiment
[0203] FIG. 21 shows a schematic construction of the driving
circuit for an optical scanner of the fourth embodiment in the
present invention.
[0204] In addition to the construction of the driving circuit for
an optical scanner of the third embodiment shown in FIG. 16, the
driving circuit for an optical scanner of the fourth embodiment has
a first gain circuit 9 and a second gain circuit 10. In FIG. 21,
the optical scanner 1, the driving circuit 2, the detecting circuit
3, the control circuit 4, the dummy scanner 5, the dummy driving
circuit 6, the dummy detecting circuit 7, and the subtraction
circuit 8 are constructed to be identical with those in the third
embodiment of FIG. 16.
[0205] The first gain circuit 9 is configured so that the driving
command signal V.sub.d becomes I/N-fold and a resulting signal is
supplied to the dummy driving circuit 6. Here, reference symbol N
represents a positive real number.
[0206] The second gain circuit 10 is constructed so that the output
signal V.sub.n of the dummy detecting circuit 7 is increased N-fold
and a resulting signal is supplied to the subtraction circuit
8.
[0207] Subsequently, reference is made to the flow of the signal in
the driving circuit for an optical scanner of the fourth
embodiment.
[0208] When the driving command signal V.sub.d is output from the
control circuit 4, the value of the signal supplied to the dummy
driving circuit 6 by the first gain circuit 9 becomes V.sub.d/N,
and the signal level of the driving signal (the alternating
current) supplied to the dummy driving coil 502 becomes 1/N. As a
result, the mutual induction electromotive force e.sub.r induced to
the dummy sensor coil 503 also becomes 1/N. This is because the
mutual induction electromotive force e.sub.r, as shown in Eq. (11),
is proportional to the current flowing through the dummy driving
coil 502. The mutual induction electromotive force e.sub.r is
changed by the dummy detecting circuit 7 into a detecting signal
V.sub.n/N, which is increased N-fold and is delivered to the
subtraction circuit 8.
[0209] Thus, according to the driving circuit for an optical
scanner of the fourth embodiment, when the value of N is set to be
1<<N in the first gain circuit and the second gain circuit,
the current flowing through the dummy driving coil 502 can be
reduced to 1/N without changing the signal V.sub.s expressing the
mutual induction electromotive force supplied to the subtraction
circuit 8. This is effective for the reduction of the power
consumption.
[0210] When N is set to be 0<N<1, the effect of the reduction
of the power consumption is lost, but the signal level extending
from the dummy driving circuit 6 to the dummy detecting circuit 7
can be increased. Moreover, the mutual induction electromotive
force can be eliminated with a high degree of accuracy and an
effect is brought about on the improvement of the S/N ratio.
[0211] If the mutual inductance is the same as the mutual
inductance M caused by the dummy driving coil and the dummy sensor
coil in the third and fourth embodiments, the dummy scanner 5 may
be constructed by using transducers as a dummy driving transducer
and a dummy sensor transducer, instead of the dummy driving coil
and the dummy sensor coil, respectively.
[0212] Fifth Embodiment
[0213] FIG. 22 shows a schematic construction of the driving
circuit for an optical scanner of the fifth embodiment in the
present invention.
[0214] In addition to the construction of the driving circuit for
an optical scanner in FIG. 5, the driving circuit for an optical
scanner of the fifth embodiment has a mutual induction component
producing circuit II and the subtraction circuit 8.
[0215] The optical scanner 1, the driving circuit 2, and the
detecting circuit 3, shown in FIG. 22, are almost the same as those
described relative to the prior art in FIGS. 3 and 5.
[0216] The mutual induction component producing circuit 11, as
shown in FIG. 23, has a phase shifter 1101 and a gain circuit
1102.
[0217] The phase shifter 1101 is constructed so that an input
signal is 90.degree. ahead in phase. Although it is desirable for
design that the phase shifter 1101 is constructed with a
second-order high-pass filter which is 90.degree. ahead in phase
with a cutoff frequency, a third- or higher-order high-pass filter
or an inverting circuit may be combined with a second- or
higher-order low-pass filter.
[0218] The gain circuit 1102 is designed to increase or decrease
the signal level of the phase shifter 1101. It is desirable that
the gain circuit 1102 is constructed so that the gain is simply
changed by the replacement of the resistance element or a variable
resistor, but it may be constructed with a variable programmable
amplifying IC.
[0219] The subtraction circuit 8 is designed to subtract the output
of the mutual induction component producing circuit 11 from the
output of the detecting circuit 3.
[0220] The control circuit 4 is adapted to control the oscillating
amplitude and frequency of the optical scanner 1 in accordance with
the output of the subtraction circuit 8. The specific configuration
and operation of the control circuit 4 are the same as in the
control circuit 4c or 4d shown in FIG. 19 or 20.
[0221] Subsequently, reference is made to the flow of the signal in
the circuit block diagram shown in FIG. 22.
[0222] From the operating controller such as a PC, not shown, the
control signal which is the command value of a desired driving
condition of the optical scanner 1, such as the oscillating
amplitude (the oscillating angle) or oscillating frequency of the
optical scanner 1, is supplied to the control circuit 4. The
control circuit 4 receives the control signal to output the driving
command signal V.sub.d to the driving circuit 2. The driving
circuit 2 sends the driving signal (the alternating current) to the
driving coil 102 in accordance with the driving command signal
V.sub.d. The optical scanner 1 is thus oscillated at desired
oscillating angle and oscillating frequency. In this case, at both
ends of the sensor coil 103, the sensor coil 103 is interlinked
with the magnetic field produced by the permanent magnets 105a and
105b and the electromotive force generated thereby is induced.
Furthermore, at both ends of the sensor coil 103, the mutual
induction electromotive force e.sub.r generated by supplying the
alternating current to the driving coil 102 is induced. Such
electromotive forces are changed by the detecting circuit 3 into
the detecting signal V.sub.s, which is output to the subtraction
circuit 8.
[0223] The control circuit 4, on the other hand, sends the same
signal as the driving command signal V.sub.d supplied to the
driving circuit 2, to the phase shifter 1101 of the mutual
induction component producing circuit 11. The phase shifter 1101 is
such that a signal V.sub.P in which the driving command signal
V.sub.d is 90.degree. ahead in phase is supplied to the gain
control circuit 1102. When V.sub.d=R.sub.0I.sub.0
sin(.omega..sub.ct) form Eq. (9), the signal V.sub.p can be
expressed as
V.sub.p=A.multidot.R.sub.0.multidot.I.sub.0 cos(.omega..sub.ct)
(20)
[0224] where A is a constant. Here, the constant A is a value
depending on a change of the signal level caused when the phase is
shifted by the high-pass filter. For example, in the case of the
second-order high-pass filter, the signal is decreased 3 dB with
the cutoff frequency, and thus the value of the constant A is about
0.708. The signal V.sub.p is sent to the gain 1102. In the gain
circuit 1102, the signal level of the signal V.sub.p is gained
(N-fold). The real number N is set so that the signal V.sub.p
coincides with the signal V.sub.n given by the following equation,
that is, the term of the signal V.sub.r of Eq. (12): 12 V n = - 2 R
2 2 R 1 + R sens e r = - 2 R 2 2 R 1 + R sens M c I 0 cos ( c t ) (
21 )
[0225] The real number N is given by 13 N = 1 A R 0 - 2 R 2 2 R 1 +
R sens M c ( 22 )
[0226] In the gain circuit 1102, the value V.sub.n
(=N.multidot.V.sub.p) in which the signal level of the signal
V.sub.p is gained N-fold is supplied to the subtraction circuit
8.
[0227] In the subtraction circuit 8, the signal V.sub.n output by
the gain circuit 1102 is subtracted from the detecting signal
V.sub.s output by the detecting circuit 3, and a resulting signal
V.sub.n-s is sent to the control circuit 4. This signal exhibits
only the electromotive force generated when the sensor coil 103 is
interlinked with the magnetic field produced by the permanent
magnets 105a and 105b. The result is that the mutual induction
electromotive force responsible for hindrance to the control of the
optical scanner 1 with a high degree of accuracy can be
eliminated.
[0228] In the control circuit 4, the subtraction signal V.sub.s-n
is monitored so that when the oscillating amplitude (the
oscillating angle) or oscillating frequency of the optical scanner
1 deviates from a desired value, the driving command signal V.sub.d
is compensated. In this way, the optical scanner 1 can be
controlled with a high degree of accuracy. In the fifth embodiment,
even when the phase shifter 1101 and the gain circuit 1102 is
replaced with each other, the same effect can be brought about.
[0229] Thus, according to the driving circuit for an optical
scanner of the fifth embodiment, the optical scanner 1 can be
controlled in regard to the amplitude or the amplitude and
frequency with a high degree of accuracy.
[0230] The driving circuit for an optical scanner of the present
invention is not limited to the application to the optical scanner
used in each of the third to fifth embodiments, and is applicable
to each of optical scanners with other mechanisms. The same effect
as in the case of the application to the optical scanner in each of
the third to fifth embodiments can be secured.
[0231] Examples of optical scanners with other mechanisms are
disclosed in U.S. Pat. Nos. 4,990,808 and 4,919,500. The
constructions of such optical scanners are described below.
[0232] FIG. 24 shows a schematic structure of another example of
the optical scanner to which the driving circuit for an optical
scanner of the present invention is applicable.
[0233] A optical scanner 1' illustrated in FIG. 24 is such that a
mirror 113 and a permanent magnet 114 are provided in series to a
torsion bar 104' connected to holders 111 to be mounted to an
arbitrary apparatus (not shown), and a driving coil 102' and a
sensor coil 103' are provided in the proximity of the permanent
magnet 114 so as to surround it.
[0234] Here, the sensor coil 103' for detecting the oscillating
angle of the torsional oscillation of the mirror 113 is provided
perpendicular to the driving coil 102'.
[0235] The driving coil 102' and the sensor coil 103' are fixed
(stationary) with respect to the permanent magnet 114 rotatable
through the torsion bar 104', and is fixed here to the holding
section of the apparatus, not shown, constructed integrally with
the holders 111.
[0236] Next, the operation of the optical scanner 1' in FIG. 24 is
briefly described.
[0237] When a driving current including the alternating-current
component is supplied to the driving coil 102', a force obeying the
left-hand rule is generated between the driving coil 102' and the
permanent magnet 114.
[0238] Since the driving coil 102' is fixed to the holding section
of the apparatus, not shown, the force obeying the left-hand rule
is applied to the permanent magnet 114, and the torsional operation
of the torsion bar 104' is performed through the permanent magnet
114.
[0239] The driving current including the alternating current is
supplied to the driving coil 102', and hence the direction of the
force obeying the left-hand rule applied to the permanent magnet
114 is changed with the alternating-current component.
Consequently, the permanent magnet 114 starts a torsional rotating
motion, with the torsion bar 104' as its center.
[0240] In the optical scanner 1 of each of the third to fifth
embodiments, the permanent magnets 105a and 105b are fixed, and the
side provided with the driving coil 102 and the sensor coil 103 is
torsion-oscillated. However, in the optical scanner 1' shown in
FIG. 24, the permanent magnet 114 and the mirror 113 are connected
in series to the torsion bar 104', and therefore the mirror 113
also executes the torsional rotating motion at the same frequency
as in the permanent magnet 114 to the torsional rotating motion of
the torsion bar 104' caused by the force of the left-hand rule
applied to the permanent magnet 114.
[0241] Thus, in the optical scanner 1' of FIG. 24, the driving
current flows through the driving coil 102' and thereby the mirror
113 can be torsion-oscillated.
[0242] When the permanent magnet 114 performs the torsional
rotating motion, with the torsion bar 104' as its center, the
magnetic field with which the sensor coil 103' is interlinked is
changed, and thus the electromotive force corresponding to the
oscillating amplitude of the torsional rotating motion is generated
in the sensor coil 103'. Whereby, the oscillating amplitude of the
torsional oscillation of the mirror 113 can be detected.
[0243] When the driving coil 102' and the sensor coil 103' of the
optical scanner 1' constructed as mentioned above is made to
correspond to the driving coil 102 and the sensor coil 103 of the
optical scanner 1, respectively, in the third to fifth embodiments,
an optical scanner in which the magnet 114 is excluded from FIG. 24
is added to the construction of FIG. 24 as a dummy scanner to use
the driving circuit for an optical scanner of the present
invention, and thereby the same effect as in the case where it is
applied to the optical scanner 1 in the third to fifth embodiments
can be obtained.
[0244] FIG. 25 shows a schematic structure of the optical scanner,
different from the optical scanner in each of the third to fifth
embodiments and FIG. 24, to which the driving circuit for an
optical scanner of the present invention is applicable.
[0245] An optical scanner 1" has the same structure as the optical
scanner 1' of FIG. 24 with the exception that the permanent magnet
114 and the mirror 113 are spaced from the single holder 111. Its
operating principle is the same as in the optical scanner 1' of
FIG. 24, and the mirror 113 can be torsion-oscillated by supplying
the driving current to the driving coil 102'.
[0246] The electromotive force according to the torsional rotating
motion, with the torsion bar 104' as its center, is generated in
the permanent magnet 114, and thereby the torsional oscillating
condition of the mirror 113 can be detected.
[0247] In the optical scanner 1" shown in FIG. 25, like the optical
scanner 1' in FIG. 24, when the driving circuit for an optical
scanner of the present invention is used, the same effect as in the
case where it is applied to the optical scanner 1 in the third to
fifth embodiments can be brought about.
[0248] According to the present invention, therefore, the mutual
induction electromotive force generated in the sensor coil can be
eliminated, so that the driving circuit for an optical scanner
which is capable of controlling the oscillating condition with a
high degree of accuracy can be provided.
[0249] Sixth Embodiment
[0250] FIG. 26 is a block diagram showing a control circuit 4e for
controlling the oscillating amplitude and frequency of the optical
scanner 1 in accordance with the detecting signal V.sub.s output by
the detecting circuit 3. The great advantage of the sixth
embodiment of the driving circuit for an optical scanner according
to the present invention lies in the circuit configuration of the
control circuit 4e.
[0251] The control circuit of this embodiment is constructed so
that the resonant frequency follow-up control is not made and the
oscillating frequency is open-controlled by the oscillating circuit
401.
[0252] The control circuit 4e has a function (an oscillating
amplitude control function) of oscillating the optical scanner 1 at
the desired oscillating amplitude (the oscillating angle) by
constructing the negative feedback loop with the amplifier circuit
403, the BPF (band-pass filter) circuit 404, the amplitude
detecting circuit 405, the subtraction circuit 406, the PI circuit
407, the gain control circuit 402, and a subtraction circuit
412.
[0253] The control circuit 4e also has a function (a constant
oscillation control function) of eliminating the oscillation of the
optical scanner 1, other than the desired oscillating motion, by
constructing the negative feedback loop with the amplifier circuit
403, an LPF (low-pass filter) circuit 410, a PI circuit 411, and
the subtraction circuit 412.
[0254] In FIG. 26, the control signal includes two command values,
the frequency command value and the amplitude command value, and
the frequency command value is first supplied to the oscillating
circuit 401. In the oscillating circuit 401, a sine-wave signal
with a preset amplitude at a frequency indicated by the frequency
command value, or a rectangular wave (a pulse wave) including a
sine-wave component, is produced and is output to the gain control
circuit 402. In the gain control circuit 402, the amplitude of the
sine-wave signal (or the rectangular or pulse wave including the
sine-wave component) output from the oscillating circuit 401 is
controlled in accordance with the control signal output from the PI
circuit 407, and a resulting signal is output to the subtraction
circuit 412.
[0255] The amplifier circuit 403 is designed to increase the
amplitude at a preset factor in order to facilitate the control of
the signal level (signal amplitude) of the detecting signal V.sub.s
and to supply a resulting signal to the BPF circuit 404 and the LPF
circuit 410.
[0256] The BFP circuit 404 is constructed with a band-pass filter
which extracts only the oscillating frequency component (the
frequency component indicated by the frequency command value).
Where a high-frequency noise lessens, the BPF circuit 404 may be
constructed with an HPF (high-pass filter) circuit and in this
case, the same effect can be obtained.
[0257] The amplitude detecting circuit 405 is designed to detect an
amplitude value (or an RMS value) of the supplied signal so that a
resulting detecting signal is output to the subtraction circuit
406. The subtraction circuit 406 is adapted to find a deviation
between an amplitude value obtained by the amplitude detecting
circuit 405 and an amplitude command value which is the control
signal so that a resulting deviation signal is output to the PI
circuit 407. The PI circuit 407 has an I circuit (an integrating
circuit) an a P circuit (a proportional circuit) so that the
deviation signal output from the subtraction circuit 406 is
amplified by a preset gain and a resulting control signal is output
to the gain control circuit 402.
[0258] The LPF circuit 410 is constructed with a low-pass filter
which extracts only the frequency component lower than a desired
oscillating frequency (a frequency indicated by the frequency
command value). The PI circuit 411 is designed to apply a desired
gain to a low-frequency component extracted by the LPF circuit 410
and has an I control circuit (an integrating circuit) and a P
control circuit (a proportional circuit). The PI circuit 411,
unlike the common PI circuit such as the PI circuit 407, has gain
characteristics in which the gain of a DC component is suppressed
by the P control as shown in FIG. 28A. It is for this reason that,
as seen from Eq. (8), in the DC region in which the frequency f is
zero, the electromotive force V.sub.r generated in the sensor coil
103 becomes zero, that is, the DC operation of the mirror portion
101 cannot be detected by the sensor coil 103, and thus an increase
of the gain in the DC region is responsible for degradation in
accuracy of the oscillation control of the moving plate. From this
viewpoint, when the PI circuit 411 is changed to a circuit adding
gain characteristics such as those shown in FIG. 28B, namely a D
control circuit (differentiating circuit), a further effect is
brought about. The output (that is, the control signal) of the PI
circuit 411 is supplied to the subtraction circuit 412. In the
subtraction circuit 412, the output of the PI circuit 411 is
subtracted from the output of the gain control circuit 402, and a
resulting signal is output as the driving command signal
V.sub.d.
[0259] Subsequently, reference is made to the operation of the
control driving circuit of the optical scanner shown in each of
FIGS. 3, 5, 6, and 26.
[0260] In the initial condition where the optical scanner 1 is not
oscillated, the frequency command value of the control signal is
supplied to the oscillating circuit 401. In the oscillating circuit
401, a sine-wave signal with a preset amplitude at a frequency
indicated by the frequency command value, or a rectangular wave (a
pulse wave) including a sine-wave component, is produced and is
output to the gain control circuit 402.
[0261] On the other hand, the output V.sub.s of the detecting
circuit 3 is zero and the amplitude command value of the control
signal is supplied to the subtraction circuit 406. Hence, the
output of the subtraction circuit 406 becomes plus and the control
signal produced in the PI circuit 407 is increased. As a result,
the optical scanner 1 starts the oscillating motion at the
frequency indicated by the frequency command value, and the gain
control circuit 402 is operated to increase the oscillating
amplitude of the optical scanner 1 until the output V.sub.s of the
detecting circuit 3 agrees with the amplitude command value (until
the output of the subtraction circuit 406 becomes zero).
[0262] Conversely, where the output V.sub.s of the detecting
circuit 3 exceeds the amplitude command value, the gain control
circuit 402 is operated to decrease the amplitude of a sine wave (a
rectangular wave or pulse wave) signal output from the oscillating
circuit 401 and to decrease the oscillating amplitude of the
optical scanner 1.
[0263] In this way, the control circuit 4e is capable of performing
the oscillating motion of the optical scanner 1 at a desired
oscillating amplitude. That is, even though the oscillating
amplitude of the optical scanner 1 fluctuates as shown in FIG. 9A,
this fluctuation can be compensated.
[0264] Here, it is assumed that the oscillating motion of a low
frequency, such as that shown in FIG. 9B, other than the
oscillating motion of the frequency indicated by the frequency
command value is applied to the optical scanner 1. In doing so, the
sensor coil 103 detects the oscillation of the low frequency, and
the signal of its low frequency component is added to the output
V.sub.s of the detecting circuit 3.
[0265] In the control circuit 4e of the sixth embodiment, by
contrast, the signal of the low frequency component is extracted by
the LPF circuit 410 and is supplied to the PI circuit 411. In the
PI circuit 411, this signal is amplified by a preset gain and a
resulting signal is delivered to the subtraction circuit 412.
[0266] In the subtraction circuit 412, the output of the PI circuit
411 is subtracted from the output of the gain control circuit 402
in order to cancel the low-frequency oscillating motion of the
optical scanner 1. Thus, in the control circuit 4e, even though the
low-frequency oscillation, such as that shown in FIG. 9B, is added
to the oscillating motion of the optical scanner 1, this motion can
be compensated.
[0267] Seventh Embodiment
[0268] The seventh embodiment of the driving circuit for an optical
scanner according to the present invention is characterized by the
circuit configuration of a control circuit 4f shown in FIG. 27.
[0269] The control circuit 4f of this embodiment has a function (a
resonant frequency follow-up control function) of oscillating the
optical scanner 1 at the mechanical resonant frequency f.sub.c by
constructing the positive feedback loop, unlike the control circuit
4e of the sixth embodiment, with the amplifier circuit 403, the BPF
circuit 404, the phase-shifting circuit 408, the gain control
circuit 402, and the subtraction circuit 412.
[0270] The control circuit 4f also has a function (an oscillating
amplitude control function) of oscillating the optical scanner 1 at
a desired oscillating amplitude by constructing the negative
feedback loop, like the control circuit 4e of the sixth embodiment,
with the amplifier circuit 403, the BPF circuit 404, the amplitude
detecting circuit 405, the subtraction circuit 406, the PI circuit
407, the gain control circuit 402, and a subtraction circuit
412.
[0271] The control circuit 4f, like the control circuit 4e of the
sixth embodiment, further has a function (a constant oscillation
control function) of eliminating the oscillation of the optical
scanner 1, other than the desired oscillating motion, by
constructing the negative feedback loop with the amplifier circuit
403, an LPF (low-pass filter) circuit 410, a PI circuit 411, and
the subtraction circuit 412.
[0272] The phase-shifting circuit 408 is designed to make phase
adjustment so that the driving command signal V.sub.d output from
the gain control circuit 402 agrees in phase with the detecting
signal V.sub.s supplied to the amplifier circuit 403 (because both
signals agree in phase with each other in the oscillation at the
resonant frequency), and is constructed so that the signal is
delivered to gain control circuit 402 by shifting the phase of the
output of the BPF circuit 404. Also, the amount of phase adjustment
made here is governed by the amount of phase shift at each of the
amplifier circuit 403, the BPF circuit 404, the gain control
circuit 402, and the subtraction circuit 412. The construction
other than the above description is the same as in the sixth
embodiment, and thus its explanation is omitted.
[0273] Subsequently, for the control driving circuit of an optical
scanner shown in FIG. 27, a description is given of the operation
with respect to only the resonant frequency follow-up control
function which is peculiar to the seventh embodiment.
[0274] In the initial condition where the optical scanner 1 is not
oscillated, since the output V.sub.s of the detecting circuit 3 is
zero and the amplitude command value of the control signal is
supplied to the subtraction circuit 406, the control signal
produced in the PI circuit 407 is increased (a negative feedback
gain becomes at least 1). As a result, the loop constructed with
the amplifier circuit 403, the BPF circuit 404, the phase-shifting
circuit 408, the gain control circuit 402, and the subtraction
circuit 412 satisfies an oscillating condition, and the optical
scanner 1 starts the oscillating motion at the resonant frequency.
The gain control circuit 402 is operated to increase the
oscillating amplitude of the optical scanner 1 until the amplitude
value of the output V.sub.s of the detecting circuit 3 agrees with
the amplitude command value (until the output of the subtraction
circuit 406 becomes zero).
[0275] Conversely, where the amplitude value of the output V.sub.s
of the detecting circuit 3 exceeds the amplitude command value, the
gain control circuit 402 is operated to decrease the oscillating
amplitude of the optical scanner 1.
[0276] In the control circuit 4f, the optical scanner can thus be
always driven at the resonant frequency, and the oscillating
condition of the optical scanner 1 can be controlled, with a high
degree of accuracy, by the oscillating amplitude control and the
oscillation stabilizing control.
[0277] Also, although the driving circuit for an optical scanner of
the present invention is not limited to the application to the
optical scanner used in each of the sixth and seventh embodiments,
it can be applied to each of optical scanners constructed by other
mechanisms, and the same effect as in the case where it is applied
to the optical scanner in each of the above embodiments can be
obtained.
[0278] Examples of optical scanners with other mechanisms, as
described with reference to FIGS. 24 and 25, are disclosed in U.S.
Pat. Nos. 4,990,808 and 4,919,500.
[0279] For the structure and function of such an optical scanner,
the explanation is omitted to avoid repetition. However, when the
driving circuits for an optical scanner of the sixth and seventh
embodiments are applied to the optical scanners with these other
mechanisms, as will be understood from the description of the third
to fifth embodiments with reference to FIGS. 24 and 25, the
oscillating motion of the optical scanner, other than the desired
oscillation, can be eliminated, and high-precision amplitude
control becomes possible. As a result, the driving circuit for an
optical scanner in which an optical scan with permanent stability
is possible can be provided.
[0280] Eighth Embodiment
[0281] The driving circuit for an optical scanner of this
embodiment, in which the detecting circuit 3 is constructed as a
detecting circuit 3-d shown in FIG. 29, is characterized by the
configuration of this detecting circuit. What follows is a
description of the circuit.
[0282] In the detecting circuit 3-d shown in FIG. 29, reference
numeral 331 represents a constant-voltage source (V.sub.e)
connected in series to the sensor coil 103.
[0283] A detecting circuit block 330 has exactly the same
configuration as the detecting circuit 3-a of FIG. 6, and the its
output V.sub.o is given by 14 V o = - 2 R 2 2 R 1 + R sens ( V r -
V e ) ( 23 )
[0284] Reference numeral 332 represents a BPF (band-pass filter)
eliminating a DC voltage component (namely, the term of V.sub.e)
from the output V.sub.o of the detecting circuit block 330
expressed by Eq. (23), and its output V.sub.s is as shown in Eq.
(10).
[0285] The BPF 332 is used for the purpose of eliminating the DC
voltage component (the term of V.sub.e). Thus, a HPF (high-pass
filter) may be used as a such a filter instead of the BPF.
[0286] Reference numeral 333 denotes a LPF (low-pass filter)
extracting the DC voltage component (namely, the term of V.sub.e)
from the output V.sub.o of the detecting circuit block 330
expressed by Eq. (23), and its output V.sub.h is expressed as 15 V
h = 2 R 2 2 R 1 + R sens V e ( 24 )
[0287] As seen from this result, the output V.sub.h of the LPF 333
is a signal indicating the resistance value of the sensor coil
103.
[0288] Therefore, when the output V.sub.h of the LPF 333 is
monitored by the operating controller such as a PC, not shown, it
becomes possible to see how the detecting signal V.sub.s is
influenced by the fluctuation of the resistance value of the sensor
coil 103. Moreover, since the coefficients of Eqs. (10) and (24)
are exactly the same, it is also possible to see the influence on
the fluctuation of each of the operational amplifier and the
resistance elements constituting the detecting circuit block 330.
When the control signal supplied to the control circuit 4 is
compensated in accordance with the extent of the influence, the
optical scanner 1 can be controlled with a high degree of
accuracy.
[0289] Ninth Embodiment
[0290] The driving circuit for an optical scanner of this
embodiment, in which the detecting circuit 3 is constructed as a
detecting circuit 3-e shown in FIG. 30, is characterized by the
configuration of this detecting circuit. What follows is a
description of the circuit.
[0291] In FIG. 30, the detecting circuit 3-e has the same
construction as the detecting circuit 3-d of FIG. 29 with the
exception of a component denoted by reference numeral 340, which is
a divider for dividing the output of the BPF 332 by the output
V.sub.h of the LPF 333. The detecting circuit 3-e has the output of
the divider 340 as the signal V.sub.s, which is given, from Eqs.
(10) and (25), by 16 V s = - 2 R 2 2 R 1 + R sens V r 2 R 2 2 R 1 +
R sens V e = - V r V e ( 25 )
[0292] As seen from this result, in the output V.sub.s of the
divider 340, the influence on the fluctuation of each of the
operational amplifier and the resistance elements constituting the
detecting circuit block 330, as well as the resistance value of the
sensor coil 103, is eliminated.
[0293] Thus, when the output V.sub.s of the detecting circuit 3-e
(the output of the divider 340) is used, the optical scanner 1 can
be controlled with a high degree of accuracy.
[0294] In the ninth embodiment, the detecting circuit block 330 has
exactly the same configuration as the detecting circuit 3-a of FIG.
6, but even though it has the same configuration as the detecting
circuit 3-b of FIG. 10 or the detecting circuit 3-c of FIG. 11, the
same effect can be secured. This reason is as follows: In the case
of the detecting circuit 3-b of FIG. 10, the output V.sub.o of the
detecting circuit block 330 is given by 17 V o = - R 4 R 3 + R sens
( V r - V e ) ( 26 )
[0295] and in the case of the detecting circuit 3-c of FIG. 11, the
output V.sub.o of the detecting circuit block 330 is given by 18 V
o = R 5 R 5 + R sens ( V r - V e ) ( 27 )
[0296] In either case, as in the case where the output V.sub.s of
the divider 340 is found by Eqs. (23)-(25), the output V.sub.s of
the divider 340 is such that the influence on the fluctuation of
each of the operational amplifier and the resistance elements
constituting the detecting circuit block 330, as well as the
resistance value of the sensor coil 103, is eliminated.
[0297] In the ninth embodiment, the direction of connection (the
polarity direction) of the constant-voltage source 331 is set to be
plus (+) on the side of the sensor coil 103, but even though it is
reversed, the same effect can be obtained.
[0298] Also, the driving circuit for an optical scanner of the
present invention is not limited to the application to the optical
scanner shown in FIG. 3, and it is also applicable to each of
optical scanners with other mechanisms described with reference to
FIGS. 24 and 25. In this case also, the same effect as in the case
of the application to the optical scanner in each embodiment can be
brought about.
* * * * *